PTrap too far below sink .??

Hello and thanks in advance,

Just curious if a Ptrap can actually be installed too far below a sink and if so could that cause the force/speed of the water dropping down to leave the ptrap unfilled and letting sewer gas into the house?

We are getting some terrible smells from the sinks from time to time and can not think of what else the problem could be. The smell is not constant which makes me think the above might be happening.

We turned a piece of furniture into a sink and wanted to try and preserve the drawers below so we is put a 90 on the sink drain and ran that towards the back of the wall and then down to a trap, basically we went over and around the drawers so we could still use them..

Thanks and good weekend to all.

The length of the piping to the trap could become fouled and create the odor also.

If the tailpiece is too long, it will siphon a trap. Is there a vent on this lav? Normally the vent takes off at the height of the p-trap traparm.

Seem to remember 2' as a max fall on a sink before the trap, but don't quote me on that! As mentioned, the trap not only stops sewer gases but also decaying crud that may be accumulating on the interior of the pipe up to the trap. The longer the pipe to the trap, the more area that can accumulate hair, soap scum, etc.

I doubt very much that your drain configuration is causing the problem. I assume (because you left out that info) that your trap is somewhere
on the same floor, behind the drawers? I have done similar drawer-dodging setups before with no problems. Also, the drain routing is not all
that different than one frequently finds in dual-sink configurations. I would look to a venting problem that is sometimes causing the trap
to siphon. I have never encountered "terrible smells" from the usual gunk that collects on inner pipe walls, but I suppose there is wide variation
in the sort of stuff people dump down their sink drains.

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I suppose there is wide variation in the sort of stuff people dump down their sink drains.

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Sometimes it's in the bathroom sink itself. If there is an overflow, it drains down to the pop-up drain. I've seen people force water down the overflow with some bleach to clean that.

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Originally Posted by jadnashua

Seem to remember 2' as a max fall on a sink before the trap, but don't quote me on that! .

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Sounds good with the exception of washing machine standpipes which can usually be 30".

Had these diagrams saved.

The outlet of a WM is pumped, and the increased velocity would tend to scour the pipe with each use, not the same case as with a sink, draining via gravity, especially if a large portion of it was horizontal.