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Do Bathroom Sinks Need a P Trap? (Explained)

If you are wondering what that P-looking pipe does for your sink, you may be relieved to know that it’s what keeps all the gunky smell away. P traps under your bathroom sinks are necessary. Here is why.  

Do bathroom sinks need a p trap?

Bathroom sinks certainly need a p trap for preventing toxic sewage gasses from entering the household. Other than that, u bend in the p trap also helps to catch anything that falls. Additionally, a p trap makes sure that the piping system does not get clogged.

Do all bathroom sinks need a p trap?

All bathroom sinks need a p trap in order to keep those sewer gases at bay. Many people also go for S traps, but s traps tend to become dry over time. P traps are easy to maintain and can be used to keep the drain system clog free.

Why do bathroom sinks need p traps?

Under your bathroom sink, some pipes connect to the wall. The rest from there is a whole drainage system that happens to connect to the sewers.

There are precisely 3 important roles a p trap under the sink plays out and here are the good ones on why they are needed after all:

To catch what falls:

If we asked you to raise your hand if you ever dropped something down the sink, we’d probably have everyone with their arms in the air. A p trap under your bathroom sinks helps to prevent that object from being washed out.

Whether you have dropped a coin or your expensive wedding ring, you’ll have to trust the p trap to hold onto it. All you have to do is turn off the tap so that no more water flows down the system.

It will also prevent your drain system from clogging now and then as it will stop the solid, bigger debris from flowing further down the pipe. If your pipes are clogged, you would notice your sink soon overflowing.

To bring out the object from the trap, keep a bucket under the working area. As you unbolt the nuts, bend the p trap so that the object can come out and be dropped into the bucket.

Be sure to attach the p trap back into the drain system and check for leaks.

To protect from toxic gases:

At this point, if you think a p trap’s only purpose is to catch falling objects, you might think it is not as necessary as we are claiming it to be. However, more than that, the trap has a more important task to do.

As the p trap has a u-shaped structure, the curved part collects water. Since the drain system of all sinks, whether it is a bathroom sink or a kitchen sink, connects all the way to the main sewer system.

From there sewer gasses travel up the pipes, and towards the sink. The p trap of accumulated water stops these gases from entering our homes.

These sewer gases are toxic, and inhaling them, in the long run, can cause many health problems for your family members and pets alike.

The sickness can be as bad as a headache and, for some, it could also cause breathing problems in the long run.

To keep the odor away:

What else comes from the sewer lines other than the toxic gases? This is of course a no brainer, as we have all tolerated the horrible smell of sewage leaks, at least once in our lives.

If the p trap had not been there to trap the gases, you would constantly be annoyed by the very smell. That smell alone is also capable of making people feel nauseous, dizzy, and lose appetite for food.

Can I use a 1 1/2 p trap for the bathroom sink?

For bathroom sinks, the typical size for the p trap that is used is 1 1/4 inches, whereas, for kitchen sinks, 1 ½ inches p traps are used.

As a rule of thumb, if the drain hole of the bathroom sink is 1 ½ inch, only then you can use a p trap of 1 1/12 inches. Generally, bathroom sink drain holes are designed to a 1 ¼ inches and hence the same sized p trap must be used.

What size p trap do I need for the bathroom sink?

Typically, as most bathroom drain holes are 1.25 inches, you would require a p trap that is 1.25 inches as well. However, each sink or connection requires a different size trap.

Here is a list of different trap sizes according to place and use:

Spot P trap size in inches
Bathroom sink1.25
Kitchen sink1.5
Washing machine2
Laundry tub opening1.5
Floor drain pipe2
Bathtub sink1.5

How to install p trap for the bathroom sink?

P trap under your sink is of vital importance, and in case you don’t want to spend extra cash on plumbing costs, you may learn how to install one if you don’t have one already. Here are a few steps you should follow:

Find the sides:

Since the p trap has a longer side and a shorter one, you’ll first have to find the shorter side and also the straight pipe that connects from the bottom of the sink, downward. Connect these two ends together.

Adjust the fitting:

Now, adjust the fitting of the P trap against the tailpiece.

To make sure that the other end of the p trap is also lined up against the opening in the wall, you can either use tools like a hacksaw or change the size of the tailpiece.

Check the alignment:

Recheck the alignment again as this could break your efforts to install the p strap.

Now slide the wall end of the p trap to the opening drain and fit it securely to the end. The p trap should neither be too long nor too short between the two points.

Slide in the nuts:

Now after the alignment is confirmed, slide in the nuts accordingly. Next, carefully screw the ends to the tread. In order to tighten the nuts, use pliers.

Check the nuts if they are screwed properly:

For the final step, you would have to check if the slip nut is properly screwed or has leaks. For that, turn on the faucet tap at full speed, and let the water run for a while.

If you notice leaks, use adjustable pliers to make sure nuts are tightened. However, it is worth noting that over tightening the nuts can damage them.

How to align the sink drain with the p trap?

To align the sink drains with the p trap, first, you need to insert the shorter end of the p trap to the sink tailpiece and the other to the wall drain opening.

When in position, you would want to slide in the p trap into the wall opening until it stops itself. Now slide the trap out until it attached itself with the sink tailpiece opening.

The p trap should exactly sit between the two points like a puzzle piece. If it’s longer or shorter, you would have to cut it into the size or get another p trap.

Is there an alternative to AP trap?

The S trap, as named for its shape, can be an alternative to a p trap under bathroom sinks. Although they are made to do the same work, an S trap causes the drain to become dry and hence cause gas leaks.

If p traps are not installed correctly, they would do more harm than good. They become a possible leak for sewer systems instead. For this reason, many look for alternatives to a p trap.

Does a bathroom sink need a u bend?

U bend under a bathroom sink is necessary for a few good reasons. The U bend in the shape that a p trap has where deposited water helps to stop sewage gas from entering the house.

Without a u bend, toxic gases would cause health problems for the people living inside the house. The U bend also helps to ward off bad smells from the drains.

How do you tell if a bathroom sink drain has a trap?

If you want to find out if your sink drain has a trap, you would first have to pour some water.

Next, you have to detach the drain and check to see if there is water deposited in the pipe. If you notice there is water, your sink has a trap.

Do bathroom sinks come with drains?

A typical bathroom sink always comes with a drain. You may want to turn on the water, disconnect the drain and check if yours has one too.

However, you would not find integrated drains in shower or tub drains as with sinks.

Do all bathroom sinks have 3 holes?

Most bathroom sinks have a 3-hole system, where one of the holes is for sprout and the others are for faucet handles.

Most, for bathrooms, the common sizings are 6”, 8” or 6”-16”. It is possible, still, to use 2-hole faucet systems in a 3-hole sink.

Final Thoughts:

The drain system under your bathroom sink is made in such a way that no sewage gasses can enter through the sink into our homes. Without a p trap, the horrible odor of these toxic gases would make it impossible for one to continue living under that roof. A P trap should also be installed properly.