Does A Dishwasher Need A P Trap?

Are you unsure if your dishwasher needs a P trap?

Did you know a P-trap prevents water back-flow and clogging in your dishwasher?

If you’re working on installing or troubleshooting a dishwasher, understanding whether it needs a P-trap is essential. Don’t worry. We’ve got you covered.

In this article, we’ll delve into the significance of a P-trap for dishwashers, where it should be installed, and whether it is required according to plumbing standards.

Keep reading to discover the importance of a P trap and how it contributes to the proper functioning of your dishwasher’s drainage system.

What is a Dishwasher Back-flow Preventer?

A dishwasher back-flow preventer is a plumbing component primarily incorporated to prevent sewer gases from rising to the dishwasher. These gases include methane, sulfur dioxide, ammonia, and more.

A P-trap that forms a U-shaped barrier is commonly used as a back-flow preventer in plumbing. However, these component does more than prevent gas pollution. Some of its other advantages are;

  • Trap debris and clogs would cause clogging, resulting in environmental pollution due to overflow. Thus, the U-shape holds these materials and has a well-designed outlet that you can open for emptying. 
  • Protect against accidental loss of property. This is not the reason for the construction of this component. However, if your jewelry, such as rings or necklaces, accidentally slips into the sink, the p-trap prevents it from draining into the sewer.
  • Prevents bad odor. The p-trap is designed to trap water on its curves. Every time you open the tap, the old water on the trap is flushed out and replaced by fresh water. Moreover, this water prevents foreign gases from flowing back into the house, which would be risky for your health.

Do You Need a Trap on Dishwasher Waste?

Yes, you need a dishwasher trap to prevent the back-flow of harmful sewer gases into the dishwasher. In most cases, plumbers take advantage of the trap connected to the sink with the dishwasher tailpiece. 

A trap is incorporated in the dishwasher drainage system to trap some water which is flushed out and filled with fresh water any time you run the inlet. The trapped water acts as a barrier to the gases from the sewer, which may try to find their way into your dishwasher.

Prolonged exposure to sewer gases, including methane and sulfur dioxide, usually results in a foul odor and health problems. These problems include lightheadedness, sinus infection, pneumonia, bronchitis, fatigue, and irritability.

Moreover, a trap on the dishwasher waste is needed to prevent clogging, usually caused by debris and clogs. That will ensure smooth and fast water flow, preventing possible health problems. 

How Do You Hook Up a P-trap on a Dishwasher?

Hooking up a trap in the dishwasher drainage system is crucial to prevent the gases from wafting into the machine. Fortunately, if you install a new drainage system, the p-trap will be included in the kit. Though they are also manufactured separately, you can still purchase them for replacement. 

Usually, p-traps are made of PVC, black ABS plastic, or chromed metal. You should always ensure the material is compatible with the existing system.

Further, they come in different sizes, from 11/4-inch 11/2-inch to 2 inches. 11 ½-inch traps are standard for sinks. Advisably, you must check the drain fitting first to get the correct drain size.

Step 1: Get the Correct P-Trap

We have already discussed what you should look at when looking for a P-trap. Briefly, ensure that the size and the material are compatible with the dishwasher or the existing drainage system.

Step 2: Test-Fit the Trap

Keeping aside the fact that you have confidence that you have bought the right trap, you need to test it before the actual installation. Hold the u-part with your hands and align it with the other pipes.

While aligning the trap, ensure it aligns with the wall pipe and the tailpiece connecting to the dishwasher.

Feel free to use a pipe cutter to cut the new arm if its length exceeds the required size to connect to all pipes. However, you should be careful not to damage the ends.

Step 3: Position the Nuts

Slip in the nut thread, followed by the nut facing downwards on the pre existing pipes. Connect the P-trap on both openings in line with the nuts and tighten them. The nuts should be tight enough to prevent leakages.

Step 4: Connect the Dishwasher Drain Pipe

Most kitchen drainage systems come with a tailpiece located just above the P-trap. A tailpiece is a narrow protruded piece of pipe where you connect the dishwasher hosepipe to drain water.

Slide in the nut threads and the nuts. Next, put the hosepipe from the dishwasher in light with the tailpiece and tighten the nuts. You can check on this demo if you have trouble assembling the dishwasher.

Step 4: Test

We trust your skills, but it wouldn’t hurt to counter-check and ensure you have done everything correctly. You can do that by running the dishwasher or opening the sink if the system is connected to one.

Look underneath at the joints to ensure that they are no leakages. If there are leakages, tighten the nuts, and you will have everything.

You can also look at this video.

Final Words

A trap is always needed for any plumbing that drains to the sewer to prevent the entry of gases harmful to your health. The trap has a U-shaped section that traps in the water, preventing the gases from flowing further.

Does it mean you must purchase a new trap anytime you get a new dishwasher? Absolutely not. The existing plumbing system from the sink has a P-trap just below the tailpiece, which connects to the dishwasher draining pipe. 

However, you can always purchase a new P-trap for replacement. When purchasing a new one, you should ensure that the size and the material are compatible with the existing system.

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