My bathroom sink drains well but the top of the water level in the drain is only about one-half inch below the hole in the sink. As the bowl gets done draining, the level in the drain moves up and down about one inch until it stops. Why is this?

Is there a "P"trap under the sink, or an "S"trap? Can you post a picture?



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it's a P-trap. I can't post a picture at this time--perhaps later if my son comes over.



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The height of the water suggests a high connection in the wall.The bobbing up and down, is just the water finding level.It sounds like someone put an elbow upward off the back side of the trap.

I don't know if this would help you visualize it, but the bottom of the sink is about 8 inches above the where the top of the trap connects to the outlet pipe.

Does the water level stay just below the drain opening indefinately? Or does it drain down over time?

It stays there indefinitely.

Then there's something that was done in the wall to create a weir, higher than the traps.That's the only explaination I can think of.

I took my shopvac and blew air through the drain and trap and the water level went down. When I turned on the faucet the water level returned to the same high level.
Could there be a vent problem?
I do appreciate your reply Paul48.

quote; top of the water level in the drain is only about one-half inch below the hole in the sink. As the bowl gets done draining, the level in the drain moves up and down about one inch until it stops.

It might be easier to answer if I knew WHICH 'hole in the sink' you are referring to. It must not be tne one in the bottom of the sink because you would not be able to see the "water level", but if it is overflow opening, that means the sink is full of water so it must not be draining very good. I am completely baffled by that last sentence. What do you mean by the "level in the drain"?

I agree with Paul48. Something in the wall plumbing is piped weird. I wouldn't worry about it if it is draining well.
Jim

I still am curious about why this is happening but I'll take advice and just stop worrying about it.
Thanks to all who responded to my post!



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To HJ:
Perhaps I should say the water level in the pipe that connects the p-trap to the sink is very close to the drain hole in the bottom of the sink.



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Water will always seek its own level. For example, one could take a clear tube and fill it with water. As you raise on end of the water filled tube, one will notice the water changing levels so that both ends of the tube are the same height.

Sailor, in your case, we presume that the drain tube going into your wall could be too high, thus keeping more water in the trap and in the drain tailpiece.

As long as your sink drains, I'd leave it as it would/could be expensive to modify it.

Is this new or has it always drained this way?

Best Wishes

this is new