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DK75 03-01-2010 10:28 PM

Reversing P-trap in bathroom sink drain?
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I am helping a neighbor install a new bathroom sink. The new sink is deeper and therefore puts the sink drain lower. I am not sure if I have the right terminology but here goes.

The sink drain feeds into the P-trap which feeds into the wall by a horizontal pipe. Now that the sink drain is lower, the P-trap will no longer fit as the horizontal drain/sewer fitting is higher than the sink drain. See attached picture. The grey PVC sink drain is 1-1/4" and the white PVC trap and sewer drain are 1-1/2".

For now I reversed the P-trap...meaning the longer leg is connected to the wall pipe, and the shorter leg is connected to the 1-1/4" sink drain. Everything is tightened up good and there are no leaks. I am concerned for the long term that the fittings are secure and tight enough to last.

Should I approach this drain configuration in a different way?

Alan 03-02-2010 09:19 AM

Technically a 4" water seal is max, so that probably is exceeding my local code anyway...

The only thing I could say might possibly work is to get a brass drain assembly because the nut would be a lot smaller, and give you quite a bit more room.

DK75 03-02-2010 01:27 PM

When you say 4" max water seal, what does this mean? Is it referring to the height of water inside the trap? I realize that this reversal of the trap increases the water column as the "legs" of the trap are now longer requiring more water to push it out and down the horizontal drain.

I will look into local code to make sure this is OK and not caught up by a home inspector. I am helping a friend remodel the bathroom in this house which will be on the market soon. I want to avoid a home inspector catching anything against code causing further issues.

I will look into alternative drain assemblies and possibly shorter ones that allow us to bring the trap back to the correct position.

All comments are greatly appreciated.

Big N8 03-02-2010 01:30 PM

I would also look into getting a new drain that is shorter.

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