Get the Johnson Pump Ultima Combo 1000: rated at 800 GPH at 3 feet of head, check valve included, and the only pick that meets ISO 8849. Most flow: Rule’s RM1100B. Lowest draw: Rule RM800B.
Top pick: Johnson Ultima Combo$92.58 at AmazonPrice as of Nov 6, 2026, 5:30 AM EST
All three are automatic 12-volt submersible bilge pumps that switch themselves on. All were new and in stock on Amazon on Oct 24, 2026 (checked through Amazon’s product data), and each scores 7.0 or higher.
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon.com at the time of purchase will apply to the purchase of this product.
How the three compare on our spec score
Five checks from each maker’s spec page and manual, equal weight. Rules and inputs are in the method section.
PlumbingPicks spec score out of 10, from Johnson Pump’s (SPX Flow) and Rule’s (Xylem) own pages and manual, read Oct 24, 2026. It is not a customer rating.
The checks are what you need to install a bilge pump right: whether the maker gives flow at real head, not just open-flow GPH, whether it names the fuse, whether it stops water draining back, how long the warranty runs, and whether it meets a named bilge pump standard. A check scores 0 when the maker doesn’t publish it.
Johnson publishes all five. Rule’s manual covers four; it names installation standards (ABYC H-22, ABYC E-11, ISO 10133) but no bilge pump product standard such as ISO 8849.
Each bilge pump, in detail
What each maker’s spec page says, what it means in a bilge, and where each lost points.
Best for real-world flow data
Johnson Ultima Combo
Johnson Pump Ultima Combo 1000 GPH automatic bilge pump, 12 V (07903-00)
1,000 GPH open800 GPH @ 3 ft3.2 A5 A fuse¾ in. hose14.4 oz
Buy it if
You want a pump whose maker tells you what it actually moves through a real hose run, with a check valve built in.
Skip it if
You need more than 1,000 GPH or a 1⅛-inch hose; Rule’s RM1100B takes 1-inch and 1⅛-inch hose.
The Ultima Combo is the bilge pump I’d put in a small boat first, and I’ve used it. Johnson Pump (SPX Flow) pairs its cartridge bilge pump with an electronic Ultima Switch for automatic operation.
The switch is the key part. Johnson says it uses patented Mirus field-effect cells that sense the water level electrically and turn the pump on and off, with no float to jam.
Johnson’s table gives flow both ways. The 1000 GPH model, 07903-00, moves 1,000 GPH straight out but 800 GPH at 3 feet of head, at 13.6 volts. It draws 3.2 amps, takes a 5-amp fuse and uses a ¾-inch connection. The table lists 16-gauge wire on its 500 GPH row.
That 20% drop from open flow to 3 feet of head is the reason the head figure matters. Every bilge pump loses flow when it has to push water up a hose and over the side.
Johnson includes a removable check valve on the 500, 750 and 1000 GPH models, says it meets the ISO 8849 marine standard, and backs it with a limited 3-year warranty.
The cartridge design means maintenance needs no tools: the pump casing stays attached to the boat and the hoses, and the motor cartridge comes out. The listing says the cartridge allows easy replacement of the motor element.
It didn’t lose a point on our checks. Its one limit is size: it weighs 14.4 ounces and stands 4.41 inches tall, per Johnson.
Johnson makes the same Ultima Combo in 500, 750 and 1250 GPH sizes and in 24 volts. The 1250 uses a 1⅛-inch outlet and doesn’t include the Dura-Port connection, per Johnson’s table.
My call: in a bilge with a long or high hose run, start from the 800 GPH head figure, not the 1,000 on the box.
1,100 GPH open806 GPH @ 3.3 ft3.8 A @ 12 V7.5 A fuse1 or 1⅛ in. hose10 ft max head
Buy it if
You want the most flow in a compact automatic pump with a sensor that can’t leave the pump running if it fouls.
Skip it if
Battery draw matters most on a boat without a charger; the RM800B draws 3.0 amps.
The RM1100B Rule-Mate is the 1,100 GPH automatic I’d pick for more flow, and I’ve used it. Rule is a Xylem brand.
Rule-Mate pumps use an internal level sensor. Rule’s product page says the 500, 800 and 1100 GPH models switch on at 2 inches of water and off at 3/8 inch; its manual gives about 2.5 inches and 5/8 inch.
Its backup feature is the reason I like it. Rule’s manual says that if the motor runs for more than 15 seconds doing little work, as when a wet paper towel blocks it, the pump stops and checks for water every 2.5 minutes instead of draining the battery.
Rule’s table gives the RM1100B 1,100 GPH at 12 volts, a 7.5-amp fuse, 3.8 amps at 12 volts and 4.8 amps at 13.6 volts. It measures 4.4 by 6 by 2.9 inches and takes 1-inch or 1⅛-inch hose. The replacement strainer is part 1232R.
Rule also lists a built-in thermal cut-off, backflow prevention that leaves less water in the bilge, and hidden air vents that help prevent air lock. It says the new impeller gives up to 10% more flow at the same amperage as older models.
Rule’s manual fills in what the product page leaves out: 806 GPH at 3.3 feet of head and 554 GPH at 6.7 feet, a 10-foot maximum head, and a 3-year warranty from the date of manufacture, with returns through the place of purchase.
Where it lost points: the manual says to install it to ABYC H-22 and E-11 and to wire it to ISO 10133, but it names no bilge pump product standard such as ISO 8849, which scored 5.
The Amazon listing’s UPC, 042237106216, matches Rule’s table for the RM1100B, so it’s the genuine pump.
Rule-Mate also comes in 500, 800, 1500 and 2000 GPH sizes, and the 24-volt RM1100B-24 draws 2.1 amps at 24 volts with a 4-amp fuse. The 1500 and 2000 models switch on higher, at 2¾ inches.
My call: at 4.8 amps on a charging system, it pulls the most here. Fuse it at the 7.5 amps Rule specifies, not bigger.
800 GPH open673 GPH @ 3.3 ft3.0 A @ 12 V5 A fuse¾ in. hose12 ft max head
Buy it if
You have a small boat or a shallow bilge, a battery with no charger, and want the lowest draw with a backup mode if the sensor fouls.
Skip it if
You need more flow; the RM1100B moves 1,100 GPH open, and the Johnson is rated at 3 feet of head.
The RM800B is the smaller Rule-Mate, and it’s the one I’d put in a small boat that lives on its battery. I’ve used it. It shares the RM1100B’s size, sensor levels and strainer, with a ¾-inch outlet and a lower draw.
Rule’s table lists it at 800 GPH open flow on 12 volts, 3.0 amps at 12 volts and 3.7 amps at 13.6 volts, with a 5-amp fuse. It measures 4.4 by 6 by 2.9 inches and takes the 1232R strainer.
Rule’s manual gives its flow at head: 673 GPH at 3.3 feet and 442 GPH at 6.7 feet, with a 12-foot maximum head. That’s a 16% loss at 3.3 feet, against 27% for the RM1100B, so the gap between the two shrinks once the hose has to lift.
It has the same fail-safe program as the RM1100B. If the motor runs for more than 15 seconds without pumping water, the pump stops and checks for water every 2.5 minutes, then goes back to normal level sensing once the debris is cleared.
Rule lists a thermal cut-off and backflow prevention. Its manual wants 16 AWG wire for a total run of up to 15 feet, counted from positive to pump and back to ground, and 14 AWG from 15 to 40 feet.
The warranty is 3 years from the date of manufacture, per the manual, and the package photo shows the same 3-year mark. Warranty returns go through the place you bought it, so keep the receipt.
The Amazon listing’s UPC, 042237106223, matches Rule’s table for the RM800B, so it’s the genuine pump.
Where it lost points: like the RM1100B, Rule names installation standards but no bilge pump product standard, which scored 5.
My call: if the boat sits for days with no charger, the lower draw matters more than the extra flow of the bigger pump.
The three pumps side by side
From the makers’ spec pages. Scroll sideways on a phone.
Rated GPH is open flow, with no hose or lift. Green marks a strength and amber a gap.
How long can your battery run a bilge pump?
Pick the pump, your battery and how far you’ll let it drain. It answers from each maker’s amp draw.
This is the question that matters on a moored boat with no charger: a bilge pump that runs all night on a slow leak can flatten the battery by morning. My call: if your pump runs every day, find the leak. A bilge pump buys time; it isn’t a fix.
Rated GPH vs what a pump really moves
Box ratings are open flow, with no hose and no lift.
Model
Open flow
At head
Drop
Johnson Ultima Combo 500 (07503-00)
630 GPH
525 GPH at 3 ft
17%
Johnson Ultima Combo 750 (07703-00)
800 GPH
700 GPH at 3 ft
13%
Johnson Ultima Combo 1000 (07903-00)
1,000 GPH
800 GPH at 3 ft
20%
Johnson Ultima Combo 1250 (08203-00)
1,150 GPH
952 GPH at 3 ft
17%
Rule RM800B
800 GPH
673 GPH at 3.3 ft
16%
Rule RM1100B
1,100 GPH
806 GPH at 3.3 ft
27%
Johnson rates at 13.6 volts; Rule tests at nominal voltage with fresh water and no ports attached, per its manual.
Both show the same pattern: every pump loses roughly a sixth to a quarter of its flow at about 3 feet of head.
Rule’s manual lists what cuts flow further: longer discharge runs, more or tighter bends, rough pipe, and restrictions such as check valves and through-hulls. My call: compare pumps at the head your hose really has, not at the box number.
How each pump senses water
All three picks are automatic, but they sense water differently.
Pick
How it senses water
On / off (maker)
If it fouls
Johnson Ultima Combo
Electronic field-effect switch (Ultima Switch)
Not stated on the page
No float to jam
Rule RM1100B
Internal level sensor
Page: on 2 in., off 3/8 in. Manual: about 2.5 in. and 5/8 in.
Checks every 2.5 minutes
Rule RM800B
Internal level sensor
Same as the RM1100B
Checks every 2.5 minutes
Neither maker uses a float on these pumps: Johnson’s Ultima Switch senses water with field-effect cells, and Rule’s sensor is built into the pump. Rule’s manual says its inlet must be placed so the pump can remove water with the boat at rest and at the worst heel and trim. My call: mount it at the lowest point of the bilge and test it there.
Wiring: amps, fuses and wire size
The makers’ numbers, side by side.
Pick
Amps at 12 V
Amps at 13.6 V
Fuse
Wire
Johnson Ultima Combo
3.2 A
Not listed separately
5 A
16 GA (listed on the 500 GPH row)
Rule RM1100B
3.8 A
4.8 A
7.5 A
16 AWG to 15 ft, 14 AWG to 40 ft
Rule RM800B
3.0 A
3.7 A
5 A
16 AWG to 15 ft, 14 AWG to 40 ft
Rule’s table shows why the charging voltage matters: the RM1100B draws 3.8 amps at 12 volts but 4.8 at 13.6, the voltage of a battery being charged.
Fuse to the maker’s number; Rule’s manual says a circuit breaker is not recommended for bilge pumps. It also says to keep every connection above the highest water level, join wires with butt connectors and a marine-grade sealant, and wire the pump to ISO 10133 and ABYC E-11.
Hose size and check valves
The outlet size sets your hose, and the hose sets your real flow.
Pick
Outlet
Check valve or backflow
Johnson Ultima Combo
¾ in. (Dura-Port)
Removable check valve included
Rule RM1100B
1 in. and 1⅛ in.
Backflow prevention built in
Rule RM800B
¾ in.
Backflow prevention built in
A check valve stops the water in the hose running back into the bilge when the pump stops, which keeps the pump from cycling on the same water.
Rule’s manual counts check valves among the restrictions that cut flow, and says to use one only to stop an automatic pump cycling on back flow.
It puts the through-hull at least 8 inches above the heeled waterline, or lower only with a seacock and a vented loop, and says a check valve must not be used to stop siphoning. It calls smooth-bore hose best and suggests two stainless clamps on the hose barb. For other water-moving pumps, our trash pump guide covers the big jobs.
Keeping a bilge pump working
My call on the routine, using the makers’ features.
Look for green corrosion at connectors and the fuse holder.
4
Check the hose
No kinks, cracks or sags that hold water.
5
Keep oil out
Rule says fresh and salt water only.
Rule’s manual says to inspect the pump, check valve and surroundings for debris periodically, and to remove the check valve and drain the plumbing when you winterize. My call: keep absorbent pads under the engine and a small spill kit on board for anything bigger.
Bilge pump vs sump pump
They look similar. They’re made for different jobs.
Bilge pump (this page)
Sump pump
Power
12 or 24 V DC from a battery
120 V AC from the house
Where
Boat hull
Basement pit
Discharge
Hose over the side
Pipe to the yard or drain
A 12-volt bilge pump is the wrong pump for a basement, and a sump pump can’t run off a boat battery. For a basement, see our sump pump basin and sump check valve size guides.
Which size for which boat
My call, not a maker chart. Bigger boats need more pumps, not just a bigger one.
Boat
Primary pump
My note
Jon boat, skiff, small tender
Rule RM800B or Johnson Ultima Combo
Low draw matters on a small battery
16–22 ft runabout or center console
Johnson Ultima Combo or Rule RM1100B
Add a manual pump as a backup
Larger boat with a cabin
Rule RM1100B
Add the high-water alarm Rule’s manual calls for
Rule’s manual says that on a boat with an enclosed cabin, an audible alarm shall warn when bilge water nears its maximum level. It also says these pumps are for the normal water an intact boat takes on from spray, rain and seepage, as ISO 15083 describes, not for flooding from hull damage.
None of these pumps is a substitute for finding where water comes in. My call: check the shaft seal, the through-hulls and the hatches first.
Mounting a bilge pump
My call on the order, using the makers’ specs.
1
Pick the low point
Mount where water collects with the boat at rest.
2
Leave room to service
Rule: an accessible spot to clean the intake.
3
Fuse it
The maker’s size; Rule: no breaker.
4
Seal the screw holes
Rule: #8 stainless, marine sealant.
5
Test it
Fill the bilge with a hose and watch it start and stop.
Bilge pumps we checked and left out
These came up on Amazon and in Google’s results.
Pump
What we found
Why it’s out
Attwood Sahara MK2 S1200 (5512-7)
Automatic float pump; flow curve, 6 A fuse, check valve and ISO 8849 in Attwood’s datasheet
Scores 8.0: Attwood’s documents give no warranty term (Amazon’s listing data says 90 days)
Rule 20SA and 25SA
Automatic pumps that check for water every 2.5 minutes
Rule’s manual for them gives fuse sizes but no flow at head; 7.0 at most
SeaSense 800 GPH automatic (10425)
Sold by Amazon.com
No maker spec sheet found
Rule 27DA, Rule 02
Non-automatic pumps
Need a separate switch; different kind
SEAFLO 06 Series 750
In stock; 3.0 A, 3.0 m max head in its manual
Scores 3.0: no fuse size, check valve or bilge pump standard on SEAFLO’s page or in its manual
SEAFLO 14A Series 1100
In stock; check valves and 13 ft max head per its listing
Not on SEAFLO USA’s site; scores 5.0 on listing facts (no fuse size or standard)
Whale Supersub Smart 1100
In stock; non-return valve, ISO 8849 (Whale’s guide)
Scores 5.0: no fuse size or flow at head in Whale’s guide; it cites a 1-year warranty
SEAFLO 06 Series 1100
Listed on Amazon
Not on SEAFLO USA’s product page
Johnson 22004 2200 GPH
Non-automatic, larger class
Different size and switching
Unbranded bilge pumps
Many listings
No maker documents
How to choose in four questions
Question
If yes
If no
Long or high hose run?
Johnson Ultima Combo (rated at head)
Keep going
Need the most flow?
Rule RM1100B
Keep going
Small boat, battery only?
Rule RM800B
Keep going
Rated by a bilge pump standard?
Johnson (ISO 8849)
Either Rule-Mate
Questions people ask
What is the purpose of a bilge pump?
It pumps water out of a boat’s bilge, the lowest part of the hull, and over the side.
What are the different types of bilge pumps?
Automatic and non-automatic electric pumps, and manual hand pumps. Automatics use a float, an electronic sensor or a timer.
What is the voltage of a bilge pump?
Most are 12 V DC; Rule and Johnson also sell 24 V versions.
What size bilge pump do I need?
My call: size for real head, not the box rating. Johnson’s 1,000 GPH pump moves 800 GPH at 3 ft.
What fuse does a bilge pump need?
Use the maker’s number: 5 A for the Johnson Ultima Combo 1000 and Rule RM800B, 7.5 A for the Rule RM1100B.
What are the common problems with bilge pumps?
Rule’s manual names debris that fouls the sensor and an air-bound pump; my call adds a clogged strainer, corroded wiring and a blown fuse.
Does a bilge pump need a check valve?
Johnson includes one and Rule builds in backflow prevention; Rule’s manual says to use a check valve only to stop the pump cycling.
How long can a bilge pump run on a battery?
Divide the amp-hours you’ll use by the pump’s amps: 50 Ah at 3.2 A is about 15 hours.
Will a bilge pump pump oil?
Rule says its pumps are for fresh and salt water only. Keep oil out of the bilge.
How do I install a bilge pump?
Per Rule’s manual: an accessible low spot, the maker’s fuse, and a through-hull 8 in. above the heeled waterline.
What does GPH mean on a bilge pump?
Gallons per hour, usually measured with no hose or lift (open flow).
Can I use a bilge pump as a sump pump?
No. Bilge pumps run on 12 V DC; sump pumps are 120 V and built for a basement pit.
How we picked these
Why trust me
I’m Isaac Daniels, a licensed journeyman plumber in Georgia (license #JP507711), and I’ve used all three picks. Specs come from Johnson Pump’s (SPX Flow) and Rule’s (Xylem) own pages and Rule’s Rule-Mate manual, read Oct 24, 2026. Where I add advice of my own, it’s labeled as my call.
How I pick
One kind of product: automatic 12-volt submersible bilge pumps from established marine pump makers, new and in stock on Amazon, checked through Amazon’s product data the same day.
Each listing was matched to the maker’s model number; Rule’s by UPC.
Each card’s spec score comes from the five checks below. All three score 7.0 or higher; a check the maker doesn’t publish scores 0.
Where the listing and the maker disagree, the maker’s number is used.
The spec score, check by check
Each check scores 0 to 10 and counts one fifth. It’s our score from maker documents, not a customer rating.
Check (weight)
How it’s scored
Flow at head published (⅕)
10 when the maker gives flow at a stated head; 5 for a maximum head only; 0 for open flow only
Fuse size published (⅕)
10 when the maker names the fuse size for the model; 0 when not
Check valve or backflow (⅕)
10 when the maker includes a check valve or lists built-in backflow prevention; 0 when not
Warranty years (⅕)
10 for 3 years or more stated by the maker; 5 for 1–2 years; 2 for under 1 year; 0 when the maker doesn’t state one
Bilge pump standard (⅕)
10 when the maker says the pump meets a bilge pump product standard (ISO 8849); 5 when it names only installation standards (ABYC, ISO 10133); 0 for none
Total
Average of the checks, to one decimal
Pick
Head
Fuse
Check
Warranty
Standard
Score
Johnson Ultima Combo
10 (3 ft)
10 (5 A)
10
10 (3 yr)
10 (ISO 8849)
10.0
Rule RM1100B
10 (3.3 ft)
10 (7.5 A)
10
10 (3 yr)
5 (ABYC, ISO 10133)
9.0
Rule RM800B
10 (3.3 ft)
10 (5 A)
10
10 (3 yr)
5 (ABYC, ISO 10133)
9.0
SEAFLO 06 750 (left out)
5 (max head)
0
0
10 (4 yr)
0
3.0
SEAFLO 14A 1100 (left out, listing facts)
5 (max head)
0
10
10 (4 yr)
0
5.0
Whale Supersub Smart 1100 (left out)
0
0
10
5 (1 yr)
10 (ISO 8849)
5.0
Attwood Sahara MK2 S1200 (left out)
10 (curve)
10 (6 A)
10
0
10 (ISO 8849)
8.0
Sources
SPX Flow, Johnson Pump Marine Ultima Combo automatic submersible bilge pump page: technical data table, dimensions, warranty, ISO 8849. Read Oct 24, 2026.
Xylem, Rule-Mate automatic bilge pump page (specification table, sensor levels, backup feature) and Jabsco/Flojet/Rule warranty page. Read Oct 23, 2026.
Xylem, Rule-Mate 500–1100 GPH instruction manual (amp.xylem.com): fuse table, wire sizes, flow at head, install and plumbing rules, warranty. Read Oct 24, 2026.
SEAFLO Marine & RV North America, 750 GPH automatic bilge pump page, SEAFLO product warranty page and the 06 Series automatic bilge pump manual. Read Oct 23–24, 2026.
Whale (Munster Simms), Supersub range installation guidelines (whale.navico.com). Read Oct 24, 2026.
Attwood, Sahara Mk2 automatic bilge pump datasheet v8 (2021), and Rule fully automatic bilge pumps manual. Read Oct 24, 2026.
Brand-written Amazon listing text for B001Q8KQFY, B07L3K5VMP, B07L3LCHYF, B013XR6W26, B09BDDS1J1, B007D2R6P0, B09B3LC5XV, B01LZSZE5O, B01LZSYF42 and B001ALYFNQ, read through Amazon’s product data, Oct 23–24, 2026.
Google results for “bilge pump”: seen Oct 24, 2026. Search volumes from Semrush, Oct 23, 2026.
