I had to remove the clean-out plug of a sink P-trap to clear a clog. Underneath, there was hardened sediment that I had to break apart with a small knife. Now that I have the drain cleared, the clean-out plug won't screw back on. I don't see any tape or rust on it and tried to clean the thread of the pipe as well. My house was built in 1947–not sure if this is original pipe or not. Is there a way to get it to screw back on? It almost seems too small at this point. Thanks.
Clean-out plug in p-trap won’t screw back on
p-trap
Related Solutions
You should be able to turn the clamp nut by the wall...
...which will allow the horizontal portion of the drain connection to pull out of the wall. It may have enough slide connection so it can be reclamped to use the existing pipe to reach the new down spout on the sink.
If it is not long enough then you will need to purchase new parts to achieve a longer horizontal portion. Do take the old pipe with you to the store so you can see what type and size of parts to place in your shopping basket.
Note that it is quite common to use a combination of the back wall slide connection and the rotation of the P-trap joint to achieve getting the pipes perfectly aligned with the sink drain. The following picture is an attempt to show how this adjustment works. There are only really two positions where there will be perfect alignment when the horizontal positioning from the wall causes the sink drain center to intersect with the arc of swing of the P-trap.
Note that if the center of the drain hole is farther from the center line of the wall pipe than the radius of the P-trap arc then there is no position where you can get things to line up. In that case then you need to use additional fittings to angle from the wall connection more toward the new drain location.
what is the best means to connect a new PVC p-trap to the existing galvanized stub out?
The plan you are proposing is best (with some things to consider, see below).
...Would ...a brass waste connector ...be better?
YES, for the reasons you (and the manufacturer) state.
...pipe dope or teflon tape ...?
I prefer tape because it is cleaner, and dope tends to harden over time and when (not if) it needs to be disassembled in the future, old hard dope is a pain sometimes.
How clean ...does the stub out need to be?
You should wire brush all old/hardened dope from the threads.
I am wondering why you are selecting an 1 1/4" trap (and wall adapter) for this job. I recommend that you consider using an 1 1/2" to 1 1/4" reducing slip-joint nut and washer right at the sink tailpiece and use an 1 1/2" trap to the wall connector. Bigger is better, unless there is some type of space limitation.
I do not recommend a clamp-on rubber boot; I have seen many of them leak. The "easiest" way is not always (in fact rarely) better.
Best Answer
This sounds like the plug in a floor drain. If so, sometimes the threads get mucked up. Often you can just clean them with some Limeaway or another decalcification product. If that's not working go to your local hardware store or HD and buy an expandable rubber drain plug. These plugs are about 1 or so inches in diameter and have a wing nut on one side and a metal washer on the other. You pop it in the drain plug hole and as you tighten the wingnut the rubber between the wingnut and the washer compresses and expands. Works like a charm.