To open a seized cast iron cleanout, soak the threads, seat a plug wrench like the Jones Stephens J40042 and turn with steady force while bracing the pipe. If the old threads are damaged, reseal with a Cherne Clean-Out Gripper, which Oatey says seals most damaged threads. Expect sewage if the line is backed up.
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This guide covers removing and replacing the threaded plug in an old cast iron drain cleanout.
Tools and plugs for a cast iron cleanout
| Product | What it does (maker) | Choose it when |
|---|---|---|
| Jones Stephens J40042 wrench | Six heads for square and slotted countersunk plugs | You need to turn a recessed brass plug |
| Cherne Clean-Out Gripper, 4 in. (270188) | Rubber threaded plug that seals most damaged threads | The cleanout threads are worn or broken |
| Cherne Clean-Out Gripper, 2 in. (270168) | Same design, 2-in. size | A 2-in. cleanout |
Older cast iron drains have cleanouts closed with a threaded brass or iron plug. After decades, that plug is often seized in place, and the cast iron threads around it can be rusted or broken. Getting it out without cracking the fitting, and resealing it properly, is the whole job.
Jones Stephens J40042: one wrench for recessed plugs
Choose the Jones Stephens J40042 to turn a countersunk plug. Jones Stephens lists (jonesstephens.com) a one-piece cast iron 6-way wrench for installing or removing countersunk plugs, drum traps and threaded cleanouts, with four heads for square plugs (0.79, 0.93, 1.16 and 1.33 inches) and two for slotted plugs (0.25 × 1 and 0.5 × 1.5 inches), and a thick enamel coating.
A recessed square or slotted plug has nothing for a pipe wrench to grab. A plug wrench seats in the recess so you can put a long handle or a pipe on it for leverage.
On October 15, 2026, the standard new offer sold by Amazon.com showed stock with part J40042.
Check Jones Stephens J40042 6-way plug wrench on Amazon →
Cherne Clean-Out Gripper: when the threads are damaged
Choose the Cherne Clean-Out Gripper when a brass plug will not seal. Oatey describes (oatey.com) Cherne Clean-Out Gripper plugs as glass-reinforced ABS with a natural rubber threaded cleanout plug that is guaranteed to seal most damaged threads, in 2, 3, 3-1/2 and 4-inch sizes (parts 270168, 270178, 270138 and 270188).
It is a practical fix when the old cast iron threads are too rusted or broken to take a new brass plug.
On October 15, 2026, the standard new offer for the 4-inch size came from a third-party seller with limited stock, part 270188, and the 2-inch size was sold by Amazon.com, part 270168.
Check Cherne 270188 4-inch Clean-Out Gripper on Amazon →
Check Cherne 270168 2-inch Clean-Out Gripper on Amazon →
Before you open a cleanout
A cleanout on a clogged line may be holding back a pipe full of sewage. If the drain is backed up, expect water to come out as the plug loosens. Put down a bucket and towels, wear gloves and eye protection, stand to the side rather than in front of the opening, and loosen the plug slowly so it does not blow out all at once.
If you are opening the cleanout to run a drain snake, have the machine set up and ready before the plug comes out, so the opening is not left uncapped longer than needed. Our drain snake types guide covers which cable fits which line. Once the line runs clear, flush it with water before you reinstall the plug.
Sewer gas comes out too; ventilate the area. Our drain cleanout guide covers where cleanouts are and which one to open.
Removing a stuck brass plug
- Clean rust and paint out of the recess so the wrench seats fully.
- Apply penetrating oil around the threads and give it time; our penetrating oil guide covers options.
- Seat the plug wrench and turn counterclockwise with steady force, using a long handle. Brace the fitting or pipe so the force does not crack the cast iron or twist the stack.
- If it will not turn, tap the plug face with a hammer to break the corrosion, then try again.
As a last resort, plumbers cut or chisel the brass plug itself, which is softer than the cast iron, and pick it out of the threads. Aim the cut at the plug, never the fitting; a cracked cleanout tee means replacing a section of pipe. Our cold chisel guide covers chisels.
Putting a plug back in
If the threads are sound, use a new brass plug sized to the cleanout and coat the threads with pipe dope or PTFE tape so it can come out next time. Our tape vs pipe dope guide explains which to use, and our pipe dope guide covers products. Snug it with the plug wrench; a drain cleanout is not under supply-line pressure, so it needs to seal, not be cranked tight.
If the threads are damaged, a rubber-threaded plug like the Cherne Clean-Out Gripper is the simpler fix than replacing the fitting.
Sizing the plug
Match the plug to the cleanout size; Cherne’s Clean-Out Gripper range of 2, 3, 3-1/2 and 4 inches reflects the common sizes. Plugs are named for the cleanout size, not the measured outside of the plug, so a measurement of the opening only gets you close. If you are unsure, take the old plug to the store and match it.
Why plugs seize, and how to prevent it next time
Brass and cast iron threads corrode together over the years, and a plug installed dry with no sealant can lock solid. Paint, rust scale and dried sewage in the recess make it worse. When you reinstall, clean the threads with a wire brush, use pipe dope or PTFE tape, and do not overtighten. Leave the cleanout where you can reach it, without drywall or a cabinet built over it, so the next person can open it without demolition.
Brass plugs come with a raised square head or a recessed (countersunk) head. A recessed head sits flush and needs a plug wrench; a raised head can be turned with an adjustable wrench.
When to call it done and when to replace the fitting
If the cleanout fitting is cracked, the threads are gone and a gripper plug will not seal, or the cast iron around it is flaking, the fitting needs to be cut out and replaced, often with a PVC cleanout and no-hub couplings. Our cast iron pipe cutter guide covers cutting the old pipe.
For PVC cleanouts, our PVC male adapter guide covers cleanout adapters and plugs.
Frequently asked questions
How do you remove a stuck cast iron cleanout plug?
Clean the recess, soak the threads with penetrating oil, seat a plug wrench and turn counterclockwise with steady force while bracing the pipe. As a last resort, cut the brass plug, not the cast iron.
What wrench fits a recessed cleanout plug?
A countersunk plug wrench such as the Jones Stephens J40042, which has four square and two slotted heads.
What if the cleanout threads are damaged?
Use a rubber-threaded plug such as the Cherne Clean-Out Gripper, which Oatey says seals most damaged threads.
Should I put pipe dope on a cleanout plug?
Yes. Pipe dope or PTFE tape seals and makes the plug easier to remove next time.
What size cleanout plug do I need?
Match the cleanout size, usually 2, 3, 3-1/2 or 4 inches; bring the old plug to match it.
How we chose
This document-based guide makes no hands-on testing claim. We read Jones Stephens’ page for the J40042 plug wrench and Oatey’s page for Cherne Clean-Out Gripper plugs. On October 15, 2026, all three linked standard new offers showed stock or limited stock. Read our selection method and about Plumbing Picks.
Primary sources
- Jones Stephens J40042 6-Way Countersunk Plug Wrench (jonesstephens.com): uses, four square and two slotted head sizes, construction.
- Oatey: Cherne Clean-Out Gripper (oatey.com): rubber threaded plug, seals most damaged threads, sizes and part numbers.