Sink drain locknut leaks

I just installed a new porcelain sink and drain assembly for the bathroom. It is leaking badly between the drain body and the locknut. It would appear that water is going past the rubber gasket and nylon washer and then between the drain body and the locknut threads.

The rubber gasket is like a flat rubber gasket with a rounded hump that should go into or up against the sink drain hole.

On my 25 year old sinks, the “hump†of the rubber gasket actually goes INSIDE the sink drain holes and sits on the flat shoulder part of the gasket. The newer rubber gasket seem to be wider and the “hump†and only goes a LITTLE inside the drain hole. To further confuse me, checking out the plumbing stores, some gaskets have a “hump†and others are cone shaped instead.

I'm guessing that the rubber gasket under pressure is sealing properly against the sink, but is NOT being pressed against the drain body and hence leaks. I'm also going to guess that the cone shaped gasket WOULD seal against the drain body. Does this make sense or not? Or rather I should just ask "what needs to be done?".

thanks.

The water is probably following the threads around and down. Smear a bit of plumber's putty or pipe dope into the threads.

LLigetfa said:

The water is probably following the threads around and down. Smear a bit of plumber's putty or pipe dope into the threads.

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thanks. Bought some pipe joint compound and that solved the drain body leak problem. Then the tailpipe leaked. More pipe joint compound and again problem solved.

Every brass thread needed to be sealed.

quote; Every brass thread needed to be sealed.

And WHY wouldn't they need sealant? They do NOT have rubber gaskets to prevent leakage. Even the locknut which leaked, even though there was a gasket, needed some assistance so the rubber would seal to the thread grooves.

hj said:

quote; Every brass thread needed to be sealed.

And WHY wouldn't they need sealant? They do NOT have rubber gaskets to prevent leakage. Even the locknut which leaked, even though there was a gasket, needed some assistance so the rubber would seal to the thread grooves.

Click to expand...

I thought this might be the best thread for asking another variation on this theme ... how's about with plastic threads? I'm installing a new American Standard "Cadet" faucet into a new American Standard sink. It has a plastic drain tube that connects to the sink by way of one largish rubber cone shaped washer and then a thin plastic flat shaped washer and then a thinish plastic tightening nut. Without any plumber's paste it seems to take a pretty tight tightening to stop a slow leaking of water. Should I put some paste on the washers and the threads? Should I tighten any more than my hand's full force? Thanks.

Put putty on the threads but it's not needed on the washer.

drain

The oil in pipe joint compounds CAN "melt" plastic, so I would NOT use it on a plastic drain fitting. They seldom leak anyway.

I think the "fear of putty" can be overdone. The drain assembly is probaly PVC. The list of chemicals which are SAFE in pvc is long.
I take my chance!
http://www.connex-electronics.com/html/products/iboco/pdf/pvc_chemicals.pdf

Thanks for the advice I appreciate it! Just to clarify the right terms, what I have here is Oatey's Great White Pipe Joint Compound w/ PTFE. It says it's safe for plastic but if there is oil in it I see how long term that could cause problems. Anyway, just wanted to make totally sure that I was using the right terms here as I get your advice about this. Thanks.