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P Trap Lower Than Drain Pipe – Configuration & Installation Guide

p trap lower than drain pipe

It is essential that the horizontal arm slopes slightly downward from the elbow to the wall drain while installing the p trap lower than drain pipe.

On other occasions, the arm will be set up perpendicularly. And proper p trap configuration should be done but never under the drain pipe.

It is necessary to either elevate the trap or down the rough-in if the P-trap is now underneath the main drain line after installing a new sink or vanity in a bathroom.

Can a P-Trap be Installed Below the Sewerage Pipe?

With a P-trap installed below the drain, the arm must be slanted to point back toward the tailpiece. Gravity-assisted water flow is impeded in this setup, which raises the possibility of backflow.

In addition, you’ll require more water pressure to flush the material down the drain, increasing the likelihood of a blockage.

P-Trap be Installed Below the Sewerage Pipe
Photo Credit: Canva

P-traps may be installed at a higher level than the wall drainage pipe. As the horizontal arm’s pitch is not more than 1/4 inch for every linear foot.

Water seals are vulnerable to being sucked out of their traps if the slope is too steep because of the increased velocity of the water.

The water will overflow if the wall drain is low and the P-trap is high. In this scenario, the P-trap may be converted into an S-trap, which is not allowed by the code.

How to Connect P Trap to Wall Drain?

If the P-trap is situated below the drain line, it may be easily fixed by lifting it. But, again, beginners should be fine with this procedure.

1. P-Trap Measurement

The sink tailpiece has to be shortened so that the P-trap may be moved up and into proper alignment with the wall stub.

The vertical component of the P-trap is connected to the tailpiece, which is the segment of pipe that extends from the sink. But first, you must determine precisely how much you want to trim.

The P-horizontal trap’s arm must be held at an angle of about 1/4 inch per foot again from the tailstock towards the wall drain as it is extended from the wall dropout to the sink drain.

Take note of where the pipe leading down from the sink drain meets the P-trap intake. The tailpiece should be snipped off here.


If you need to cut out a significant portion of the tailpiece, don’t worry about it. According to the Uniform Plumbing Code, the maximum allowable length of a tailpiece is 24 inches, but no minimum length is specified.

2. Take Out the Rear End

Even if you’ve previously set up your basin drain and P-trap, you’ll need to take out the tailpiece before you can either shorten it or swap it out for a new one. To achieve this, spin the nut counterclockwise to loosen the p trap lower than drain pipe.

To remove the tailpiece, spin it counterclockwise using tweezers or an adjusting wrench and then pull it down.

3. Remove the Tailpipe and Have it Rewired

If you want a shorter tailpiece, buy one that fits or trim the one you indicated. Make sure the replacement tailpiece is the correct size before you attempt to install it.

In such a case, you should use the hacksaw to remove the surplus portion of the pipe. Then, sand off the rough spots and replace the sink drain using a plumber’s putty to ensure a watertight seal.

4. Connect the P-Trap

The tailpiece’s length should be reduced so the P-trap can be securely attached. Ensure the P-trap fits snugly into the wall drain by testing a dry fit. If the horizontal arm is too long, you may need to trim it, just like you did with the tailpiece.

Attach the trap arm with the nut and washer. The tailpiece is then fitted with a nut and washer. The vertical end of the trap arm must be positioned over the tailpiece, and the horizontal end must be pushed into the drain aperture in the wall. You may secure the P-trap by tightening the bolts at both ends.

5. Check the Connections

For a few minutes, run the water in the sink. See whether water is leaking from the seams. Then, using a paper towel, you may check for leaks around the joints.

A pair of pliers may carefully tighten the nut at any damp joints to halt the leak. If it’s constructed of PVC, you need to be cautious not to overtighten it.


The procedure outlined above for adjusting the P-trap of a sink or vanity is universal and may be used for any drain, even that of a washing machine. It’s essential to use the appropriate-sized trap.

Alternative Methods of Connecting P Trap to Drain Pipe

If the P-trap has to be appropriately aligned and the primary drain grate is higher than the sink drain. The best way to do it is to follow the procedure outlined above. However, these options are also viable substitutes.

1. Reduce the Rough-In

Plumbing rough-ins are the water and drainage lines installed behind walls. Such as the drain line to which the p trap lower than drain pipe will be connected.

Instead of modifying the sink’s tailpiece, you may remove a section of the wall and connecting p trap to drain pipe. If you’re planning a significant upgrade to your kitchen or bathroom and don’t mind putting in a new wall panel, this may be the answer you’re looking for.

2. Put In a P-Trap that Can be Turned Around

The tailpiece of a P-trap is attached to the longer end of the bend, while the arm is connected to the shorter end.

With this setup, the trap may fill with water to a point where sewage fumes are stopped, but normal flow can continue unimpeded.

The drain will likely get clogged if a regular P-trap is reversed. It is also against the law for a trap turned upside down to retain over four inches of water. While this is the case, reversible P-traps may be available at certain hardware shops.

These traps, like other P-traps, have a J shape, yet the larger side of the curve is still small enough to provide an adequate water seal when placed with the shorter side to the tailpiece and the longer side connected to the horizontal arm.

If there is a difference in height between the sink drain and the waste pipe. A reversible P-trap should be able to solve the problem.

How to Install a Bathroom Sink Drain P Trap?

Get out your measuring tape since you’ll need to snip the wall tube down to size. A slip-joint washer must provide a watertight connection between the wall tube and the connector. Utilize the nut of the proper size with the package to pull the seal even tighter.

how to install a bathroom sink drain p trap
Photo Credit: Canva

After that, a nut and a washer are fastened onto the tailpiece linked to the fixture drain. Connect the j-bend to the tailstock before sealing the seal with an additional washer and adjusting its tension with the provided nut.

FAQs on P Trap Lower than Drain Pipe

Does it Matter where the P Trap is Located?

The ideal location is adjacent to the shower drain but not necessarily beneath it. Since hair tends to accumulate in shower drains and traps. It’s helpful if they can be accessed by a drain snake or similar instrument for unclogging.

Does P Trap have to be below Drain?

As water would generally flow downhill from the p-trap, having it below the exit drain prevents the water from doing so without some external push. 

Does the Height of the P Trap Matter?

In the United States, a washing machine’s P-trap must be installed 6-18 inches from the floor to comply with the Universal Plumbing Code. Therefore, never put a P-trap for a washing machine in a basement or attic.

How far below the Drain can the P Trap be?

The International Plumbing Code specifies that there must be no more than 24 inches of vertical space between the bottom of the sink’s drain and the bottom of the p-trap opening.

What happens if P Trap is too Deep?

Too much liquid passing through a trap too quickly may cause the seal to be sucked dry and muck to accumulate if the trap is too deep.

How long does it take for Water to Evaporate in P-Trap?

P-traps often dry out in a month but may take as little as a week. This is more common during the colder months. Keep the water moving and your P-traps from drying up by running the faucet or showers for a minute or two once a week.

Is p-Trap Supposed to be Full of Water?

A p-trap is a u-shaped curve in the drain pipe that leads from a sink to a septic tank or the city’s sewage system. P-traps, under typical conditions, always have some water in them.

Should P Trap be Directly under Drain?

It doesn’t need to be precisely beneath the shower drain; nevertheless, it should be as near to the drain as feasible. When possible, it’s preferable to have access to a drain snake or other cleaning instrument to remove hair obstructions from shower drains and traps.

Why is my P-Trap Still Leaking?

If the P trap continues to leak after these steps have been taken, there is likely a more severe problem with the trap’s fit, rust, or a missing washer, and the whole trap may need to be replaced. 

How do you Clear a Drain Past the P-Trap?

Using a funnel, gently pour up to one cup of baking soda and vinegar down the drain that has the difficult clog. This will help to break down or dissolve the blockage. Since your drain might get blocked from using too much baking soda, it is best to alternate between the two.

P Trap Lower than Drain Pipe: Conclusion

The information in this blog post will help you understand the basic configurations and Installation of a p trap lower than drain pipe. This is an essential part of ensuring that your plumbing system works properly. By following the instructions in this article, you can be sure that your p trap will be installed correctly and efficiently.

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