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P-Trap Lower Than Drain Pipe

There are a bunch of things you need to get right when knocking out a plumbing project at your home – but making sure that the p-trap sits in the right spot (especially in relation to your drain) is a major piece of the puzzle.

A p-trap sitting lower than your drain pipe is a common issue that homeowners and remodelers run into when they are adding new sinks into existing plumbing setups. Having your p-trap sit lower than your drain pipe is a bit of a nightmare scenario, though. It can easily cause water to come flushing out of the trap itself rather than flowing through your plumbing as it should.

Below we run through (almost) everything you need to know about your p-trap system, where it needs to be positioned in relationship to your drain, and how to fix this problem if things go sideways on your plumbing project.

P-Trap Lower Than Drain Pipe – Is That a Problem?

Yes, having a p-trap sit lower than your drain pipe is a problem – a big problem, even. Unless of course, you want everything that goes through your drain (water, waste, everything) to come flooding out into your cabinets and then eventually onto your bathroom floor.

We’re joking, obviously.

If the p-trap sits below your drainpipe, though, that’s exactly what you are going to be dealing with.

For one thing, the odds are pretty good that your plumbing isn’t going to line up correctly if the p-trap is sitting in the wrong spot. You’ll end up having gaps that water can flow right out of.

Secondly, if the p-trap sits below the exit drain you’re going to have to rely on gravity to pull water through the system rather than allowing the drain to work all on its own.

Worse, you’re likely going to compromise the actual effectiveness of the p-trap itself – a system intended to stop all kinds of funky smells bubbling up through your sink from the rest of your wastewater plumbing system.

No, you want to be sure that you’ve got your p-trap in the right place for it to do its job as intended. The p-trap should always be positioned slightly higher than the drain pipe.

How Close Does the P-Trap Need to Be to the Drain?

While there aren’t any real rules (or international building codes, for that matter) that influence how close your p-trap has to be in relationship to your drain or your wall, the codes do talk about the maximum distance that the p-trap can be from the drain itself.

The International Plumbing Code states that you need to have your p-trap located no more than 24 inches away from the drain itself. Any further away than that and the p-trap immediately begins to lose effectiveness.

It’s generally a good idea to keep your p-trap as close to your drain as possible while still allowing it to function the way it was designed. Your plumbing, drain system, and under cabinet (or vanity) dimensions are going to have a huge impact on all that.

Just keep it under 24 inches away and you’ll have nothing to worry about!

Does P-Trap Height Even Matter?

It sure does! Like we just mentioned a moment ago, if your p-trap isn’t set up in the correct spot it either isn’t going to hold water the way it should (creating that airtight gap that seals away noxious and possibly toxic gases) but it’s also not going to allow the drain system itself work the way that it’s supposed to.

When your p-trap is located below the drain the natural flow of water (which always wants to seek the lowest possible surface) is going to be impeded – maybe just a little bit, but maybe significantly. All of that depends on where your p-trap is located and just how far below the drain it is.

When the trap is set up correctly, though, you don’t have anything to worry about. Water is going to flow through the trap itself the way that it’s been designed to but then it’s also going to get trapped when the drain shuts off – and the rest of the water rush right out of the drain and into your wastewater plumbing.

Make sure that you install the p-trap in the right spot (or hire plumbers to handle this for you) and you won’t have anything to worry about.

How to Fix a P-Trap That’s Sitting Lower Than It Should

Any misalignment with your p-trap is going to cause a problem, ranging from mildly annoying to catastrophic. You want to avoid misalignment at all costs.

For starters, the easiest way to fix a p-trap that sitting lower than it should be is to raise it up. PVC plumbing components make this a whole lot easier these days than it ever was in the past with copper.

You won’t have to spend a ton of time cutting, you won’t have to spend a ton of time soldering, and you won’t have to tear out and replace your work if you need to start all over again (wasting a mountain of money on copper along the way).

Instead, you’ll just need to swap out different PVC parts until you get the right height and then cement them in place using pipe glue.

When you do this fix, though, make sure that your rubber seals and your rubber gaskets are in the right position. Even just a little bit of misalignment when you are tightening up your PVC screw components can cause the system to leak and fail either straightaway or later down the line.

Whatever you do, don’t just glob a bunch of silicone caulking all over the place and call it a day. That might keep you under the sink cabinet free and clear of leaks for a little while. Eventually, though, that’s going to fail and cause an even bigger mess for you to fix to square things away.

Do I Really Need to Vent My P-Trap?

Yes, you really do need to make sure that your p-trap is properly vented (and for a couple of different reasons).

For starters, proper venting guarantees that water isn’t going to be siphoned out of the trap itself when those nasty gases from the sewer climb up the plumbing system.

With the right venting in place, those gases are going to have a space to expand in without compromising the airlock of your p-trap. You won’t have to worry about back pressure breaking down your plumbing system over time – and you won’t have to worry about that nasty “glug glug” sound so common in older homes or construction without p-trap systems in place already.


When you get right down to it, making sure that you have the p-trap set up correctly is a huge piece of the puzzle.

Anytime you swap new plumbing components (especially when they’re attached to a sink) you run the risk of throwing things out of whack. Make sure that you carefully plan how your new plumbing is going to meet up to your old plumbing, keeping your trap in the right position to allow water to flow effortlessly – but also allowing that p-trap “airlock” to build up, too.