Does Garbage Disposal Need P-Trap? (Yes! Here’s Why)


You might be familiar with P-traps in various types of drains, but if you’ve never looked at the plumbing code, you may not know when they’re necessary.

Does your garbage disposal need a P-trap?

The plumbing code dictates that all drains need P-traps, so your garbage disposal needs a P-trap. A P-trap contains a pool of water that traps unsanitary and flammable sewer gasses so that they don’t come up through the drain. You’ll be able to identify the P-trap thanks to its curved, U-shaped appearance, which also looks like a sideways letter P.

In this article, we’ll talk about what a P-trap is, its function, and why your garbage disposal needs one. We’ll also discuss how to identify a P-trap and where you can find it on your garbage disposal.

Finally, we’ll provide step-by-step instructions for installing a new P-trap in a garbage disposal.

Does Your Garbage Disposal Need A P-Trap?

According to the plumbing code, the most important regulation is that every drain has to have a P-trap. This applies to toilets, which have built-in traps, tub and shower drains, sink drains, and all other drains. 

In short, yes, your garbage disposal needs a P-trap.

The function of a P-trap is to hold a pool of water that traps flammable and unsanitary sewer gases in the pipes. This way, the potentially hazardous gasses can’t make their way into the building, where people would be exposed to them.

When the P-trap was invented, it revolutionized plumbing and made bathroom and kitchen piping what it is today. In fact, modern kitchens and bathrooms likely wouldn’t exist at all without the P-trap because they wouldn’t be sanitary.

If you have a double sink, you might be stumped as to where the garbage disposal P-trap is located. But following the pipe will reveal that it does lead to a P-trap.

It may be on the other side of the cabinet, rather than being close to the disposal.

Where Is The P-Trap On A Garbage Disposal?

The P-trap on a garbage disposal is located under the sink.

You’ll be able to recognize it due to its curved U-shape. This U-shape holds water and prevents sewer gasses from moving through the piping and coming out of the drain.

How Do You Install A P-Trap In A Garbage Disposal?

Installing a P-trap in a garbage disposal is a simple project that even beginners should be able to tackle in about a half-hour.

For an overview, watch the video below. Scroll down for more detailed instructions.

Step 1: Gather Tools And Materials

You’ll need a drain trap kit as well as a bucket, tongue-and-groove pliers, a pipe cutter, rags, and a work light.

Step 2: Remove The Old P-Trap

If you’re replacing an old P-trap with a new one, you’ll need to remove the old P-trap first. Take off the curved piece or the trap bend by unthreading the slip nuts on both ends. 

Pull the trap down to detach it from the tailpiece. Dump its contents into the bucket.

Then, you’ll want to take the slip nut washer and slip nut off the tailpiece, which is the straight pipe that points down from the drain.

Depending on the configuration of your piping, there may also be an extension pipe that needs to be removed.

Next, take off the trap arm. You’ll need to loosen the slip nut that connects it to the drain pipe. Pull the arm straight out; you might need to twist it to release it.

Step 3: Check The New P-Trap’s Fit

Hold the new trap arm and bend in place to see how they line up with the wall pipe and tailpiece. You may need to use your pipe cutter to trim the new trap arm to the length of the old one. If your trap arm is too long, it can lead to clogs in the piping.

You might need to cut down the sink tailpiece with your pipe cutter as well. You can also use a hacksaw for this purpose.

Step 4: Attach Nuts And Washers

Slide a slip nut (threads facing down) onto the trap arm and place another nut on the arm’s straight end. Next, put a slip joint washer with the beveled end out on the straight end of the arm.

Put a slip nut and washer on the end of the sink tailpiece. The washer bevel should point down.

Step 5: Assemble The P-Trap

The trap arm will slide into the wall’s drain opening, and the trap bend will fit over the end of the arm and onto the tailpiece. You can also position the tailpiece extension at this point if you have one.

Slide the slip nuts against the fittings and thread them onto the hubs. 

Then, you’ll want to adjust the trap arm and bend so the pieces align properly and the arm slopes downward toward the wall. The recommended pitch is a quarter-inch per foot of downward slope.

Tighten the slip nuts by hand if they’re plastic. If you have metal slip nuts, then you can use your pliers to tighten them more.

Step 6: Test The P-Trap

Now, it’s time to turn on the faucet so that you can identify any leaks. If any of the slip nut connections start to leak, use pliers to gently tighten them.

Avoid over-tightening the nuts, especially plastic ones.

Conclusion

According to the plumbing code, all drains require P-traps because they ensure everything remains safe and sanitary. Toilets, sinks, tubs, showers, and garbage disposal drains all need to have P-traps.

This piece of piping gets its name from its appearance; it looks like a sideways letter P. If you look at a P-trap straight on, you’ll see that it has a curved U-shape to it.

The P-trap’s job is to hold a pool of water that seals flammable and unsanitary sewer gasses inside the piping. This way, these potentially hazardous gasses don’t come up through your drain.

Jessica Allen

Jessica is a freelance writer and editor who has years of experience writing about home improvement and interior design. When she’s not typing away in her office, you can find her doing yoga in her backyard or curling up with a good book.

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