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Quick answer from a licensed plumber: A dishwasher line is 3/8-inch compression at both ends, from the 3/8-inch outlet of the stop valve under the sink to a 90-degree elbow at the inlet valve. The elbow is the part that varies: 3/8-inch compression x 3/8-inch MIP for an inlet with a female pipe thread, or 3/8-inch compression x 3/4-inch female hose thread (a swivel gooseneck) for the garden-hose-style inlet Whirlpool and Bosch use. Whirlpool says to use copper with a compression fitting or a braided line, not plastic tubing, on a dedicated hot-water shut-off valve.
Covers either inlet: the Whirlpool W10278636RC 6-foot dishwasher installation kit ships both the 3/8 MIP elbow and the 3/4 hose gooseneck (Amazon-sold on September 25, 2026).
The Sizes, Once and for All
Three fittings meet under a dishwasher: the stop valve under the sink (a 3/8-inch compression outlet on nearly every angle stop), the supply line, and the inlet valve on the dishwasher itself. Whirlpool’s installation guidance states the connection its machines expect: “Connect one end to the shut-off valve and the other to the dishwasher inlet; a 3/8″ compression x 3/4″ hose fitting with a 90° elbow will be needed.” Its install kit spells out the parts: “6’ braided hose, 3/8″ comp x 3/8″ NPT male elbow fitting, 3/4″ NH x 3/8″ comp gooseneck fitting with EPDM washer, teflon tape, and instructions.” Bosch’s kit is the same shape: a “braided water supply hose (59”) with rubberized compression fittings, 90 degree elbow adaptor (3/4” x 3/8”).”
| Connection | Size | Part that makes it |
|---|---|---|
| Stop valve outlet under the sink | 3/8″ OD compression | The supply line’s compression nut |
| Supply line | 3/8″ compression both ends; 48, 60 or 72″ (BrassCraft), 6 ft (Whirlpool kit), 59″ (Bosch kit) | BrassCraft B1-DW6 “3/8 in. Comp x 3/8 in. Comp With 3/8 in. MIP Elbow” |
| Dishwasher inlet, threaded type | 3/8″ female pipe thread on the valve | 3/8″ compression x 3/8″ MIP 90° elbow (BrassCraft elbow; GE sells an “ELBOW, 3/8” NPT X 3/8”” as WS22X10032 and a “DISHWASHER 90 DEGREE CONNECTOR ELBOW” as WX28X332) |
| Dishwasher inlet, garden-hose type | 3/4″ male hose thread on the valve | 3/8″ compression x 3/4″ female hose swivel elbow (Whirlpool W10685193 “measures 3/4” x 3/8””; Bosch 3/4” x 3/8” elbow; BrassCraft “3/8 in. Comp x 3/8 in. Comp With 3/4 in. Garden Hose Elbow”) |
Which Elbow: MIP or Garden Hose?
Look at the inlet valve on the machine. If the port is a small female pipe thread, the elbow is 3/8-inch MIP into the valve, 3/8-inch compression to the hose; BrassCraft’s connector family is sorted exactly that way, “Compression x Compression with 3/8” MIP Elbow,” “FIP x Compression with 3/8” MIP Elbow,” and GE sells a 3/8-inch NPT x 3/8-inch elbow (WS22X10032) and a part it titles “DISHWASHER 90 DEGREE CONNECTOR ELBOW” (WX28X332). If the port is a fat male thread like a garden hose, you need the swivel gooseneck: Whirlpool’s genuine W10685193 is a “SWIVEL BRASS FITTING, 90-degree angle, measures 3/4” x 3/8”” and “replaces W10574777, 3288910, PS9493732, W10273460, W10273460BU, W10574777BU, W10754429 and W10829954.” A kit like Whirlpool’s ships both elbows so it covers either machine.
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The Line Itself
Whirlpool: “The supply line should be made of durable materials like copper tubing with a compression fitting or a flexible braided water supply line. NOTE: Plastic tubing is not recommended.” BrassCraft’s B1-DW6 is the braided-polymer type, “Used to connect the water supply to your dishwasher,” with “tough PVC tubing” inside, sold in 48-, 60- and 72-inch lengths, and marked “For use in potable water distribution systems in accessible locations only.” Measure the run from the stop valve to the inlet with the machine pulled out, and add slack for the machine to slide back; a 60-inch line covers most under-counter installs where the valve is under the adjacent sink.
Hooking It Up
Whirlpool’s order is the right one: locate the shut-off valve “usually found beneath the kitchen sink or along the wall,” make sure it is off, thread the elbow into the inlet with tape on the pipe threads (the garden-hose type seals on its washer, no tape), connect the line, then “Attach the dishwasher water line connection to the inlet valve, typically located at the bottom rear of the appliance. Use a wrench for a secure connection, but avoid over-tightening to prevent damage. After connecting, turn on the shut-off valve to check for leaks around the connections.” GE’s reminder for the valve: “To make sure the valve is fully open: Turn the handle counter-clockwise (to the left).”
Two more Whirlpool limits worth knowing: “The water supply should range between 20 to 120 psi,” and a machine that will not fill “might be due to a clogged filter or kinked hose. Check that the water supply valve is fully open.” The little screen in the inlet valve is the first place to look when a new line brought debris with it.
FAQ
What size is a dishwasher water supply line?
3/8-inch compression on both ends, in 48-, 60- or 72-inch lengths (BrassCraft) or a 6-foot kit (Whirlpool). One end goes on the 3/8-inch stop valve outlet, the other on a 90-degree elbow at the dishwasher inlet.
What elbow do I need for a dishwasher?
It depends on the inlet valve. A female-pipe-thread inlet takes a 3/8-inch compression x 3/8-inch MIP 90-degree elbow (the MIP elbow BrassCraft packs with its B1-DW6 dishwasher connector). A garden-hose-thread inlet takes a 3/8-inch compression x 3/4-inch hose swivel elbow (Whirlpool W10685193, which measures 3/4 x 3/8). Whirlpool’s guidance names the 3/8 compression x 3/4 hose fitting with a 90-degree elbow for its machines.
Can I use the old dishwasher supply line on a new machine?
Whirlpool says to inspect existing lines for wear or damage, and not to use plastic tubing. If the new machine has a different inlet thread, you only need to change the elbow; the 3/8-inch compression line stays the same.
Does a dishwasher need its own shut-off valve?
Yes. GE and Whirlpool both say the dishwasher needs a dedicated supply line with a shut-off valve, usually under the adjacent sink on the hot line.
Should the dishwasher be on hot or cold water?
Hot. Whirlpool specifies a hot water supply line with an ideal temperature of 120°F.
Why Trust Plumbing Picks
Plumbing Picks is written by a licensed Georgia journeyman plumber. Every part number, model list, size, setting and fit on this page comes from the manufacturer pages and documents listed below, which we opened and read; product details come from those makers and from the Amazon listings, not from hands-on testing. Each linked product was shipped or sold by Amazon, new and in stock, when we checked on September 25, 2026. Where a link goes to Amazon we may earn a commission at no extra cost to you. Nobody pays to be included here. More on who writes this and how we pick.
Sources
- Whirlpool Product Help: Dishwasher Water Supply Connection
- Whirlpool: W10278636RC Dishwasher Water Line Installation Kit
- Bosch: 11045438 Junction Box & Supply Hose Kit
- BrassCraft: B1-DW6 3/8″ Comp x 3/8″ Comp dishwasher connector with 3/8″ MIP elbow (48, 60, 72″)
- BrassCraft: Dishwasher braided polymer connectors (end-type list)
- GE Appliances: WX28X332 Dishwasher 90 Degree Connector Elbow
- GE Appliances: WS22X10032 Elbow, 3/8″ NPT x 3/8″
Bottom Line
Buy a 3/8-inch compression braided line long enough to reach with the machine pushed back, then pick the elbow by the inlet: MIP for pipe thread, 3/4 hose swivel for the garden-hose type. Tape the pipe threads only, hand plus a wrench turn, open the valve fully and check the inlet screen if it will not fill.