Plumbing Question (brass cleanout nut in PVC sink drain)

Factual Questions
1

So I’m trying to unclog/clean out my sink. It’s PVC pipe with a standard P-trap, where the bottom of the trap is accessed not by unscrewing sections of the drain pipe (they’re all cemented together) but by unscrewing a two inch or so wide PVC cap on the very bottom of the bend for the trap (the cap has a square-head flange sticking out so it can be turned using a wrench)

Except, evidently, a plumber replaced the PVC cap with some kind of (brass?) plate with a tiny (brass?) T-handle sticking out, I assume to turn the bolt holding the thing on. There’s a rubber gasket underneath the plate (actually physically above it; as this is on the bottom of the trap).

OK, makes sense (those PVC caps get all torn up by wrenches, so put something stronger in). I assumed I turn the handle to loosen everything up and pull it out. Except after turning the handle to loosen things the gasket is partly out, but won’t come out all the way, and the bolt is evidently not mated to anything anymore as turning the handle does nothing. So now I’m unable to get in, but it’s not sealed either.

Maybe I just need more force, but before I start pulling hard or doing anything drastic, can anyone point me to a diagram or description of this kind of thing, so I understand how it’s supposed to work?

2

What you’ve probably got there is an expanding “cork”. It’s a 3/4" thick rubber gasket shaped like a hockey puck but smaller & softer. The puck is sandwiched between two thin sheet metal plates of slightly smaller diameter. There’s a bolt & nut arrangement through the middle. When you tighten the bolt/nut, it draws the two plates together, causing the puck to get less thick but larger in diameter. That forms a tight seal against the female opening in your P-trap.

These kinds of plugs are used when the threads are destroyed, or for sealing unthreaded openings. I bet the former is your situation.

They don’t swell all that much when compressed. As such, to work they need to fit very snugly when installed loose. And over time the rubber stiffens. So when you release the tension on the bolt/nut, the rubber only relaxes a little and is still gripping the opening pretty tightly. As well, if the opening is threaded, even with damaged threads, those are still sharp edges that will have dug into the sides of the puck. All of these things make removing an old puck a real PITA.
Assuming I’ve diagnosed the situation correctly …

Your best bet to remove it is to 1) loosen the bolt/nut as much as possible 2) grab what of the exposed metal or puck material exterior you can with large pliers and 3) try to unscrew the whole thing as a unit from the surviving threads.

You may try “kneading” the puck a bit by squeezing it with pliers from various sides. Unfortunately, as you squeeze it from, say north to south, you’re also making it swell from east to west. So the ideal unscrewing technique is the bare minimum force necessary to keep the pliers from slipping. Bearing down on the pliers just wedges it in tighter.

In the extreme you can destroy the whole plug by removing enough of the face plate to get at the rubber and then drilling several 1/2" diameter holes upwards until the puck is reduced to a spongy mess you can dig out in pieces.
Another thought …

You’ll still need to replace the plug with a new one after this plug is out. You might want to consider now whether the smarter approach is to leave the plug in there and instead remove the entire glued-together P-trap assembly and replace it with one that’s installed properly, i.e. removably.

Your future self may thank you for taking the time to fix the job right this time. And it may be less work now to cut out and replace the P-trap than it’ll be to get that bad plug out & get a good seal on the new plug.

Good luck. DIY is so much fun.

3

That sounds like the situation exactly. Thanks!

One question: assuming there’s no time right now to do things right, and that the gasket is too far gone to be re-installed, what would it be called at a plumbing supply store?

4

The typical term is “expanding plug”. I just used Bing to search for [plumbing expanding plug] and got a lot of pix and links. They’re standard parts at any real plumbing supply shop. Although you might not find them, or not the right size, at a big box DIY store.