Traps and drains: What do they do?

Traps and drains are an important part of your home's plumbing system. Learn more about this essential integrated system that maintains a healthy ebb and flow of water in and out of your home.

Traps and drains: What do they do?

Traps and drainage pipes are an essential part of your household plumbing system. A drainage pipe moves wastewater away to the municipal sewer or septic tank. A trap makes sure that poisonous gasses and smells in the sewer don't make it back into the house. You may not be aware of your traps and drains when everything is running smoothly, but they’ll quickly make themselves known when there’s a problem.

Let's take a look at both traps and drains to better understand their function and importance.

Plumbing traps: Where are they and what do they do?

With the advent of modern plumbing came the knowledge that one pipe system was needed to bring the water into a building, and another to take the wastewater away. But how do you stop those nasty smells and gasses from the sewer or septic tank from making their way back into the house? Enter the plumbing trap.

  • Every plumbing fixture in your house – sinks, showers, toilets, dishwasher, laundry machines etc. – will have some type of trap. Traps are usually incorporated into the drainage pipes and out of sight, out of mind.
  • When there's a problem, such as a clogged drain, traps can usually be detached easily from the drainage pipe and cleaned out.

Properties of the P-trap

The P-trap is the most common household trap and found on bathroom, kitchen, and laundry sink drains.

  • The trap is typically comprised of a tailpiece, the curved trap piece, and a drain elbow.
  • The tailpiece fits into the pipe from the bathtub or sink drain, and the drain elbow is connected to the drainage pipe that goes directly into the wall.
  • A P-trap can be made of metal or plastic. While metal might be considered more durable, plastic material generally lasts longer. This is mainly because P-traps always contain a level of water, so plastic is less likely to corrode. Plastic is also easier for the homeowner to fix or replace.
  • Each time the drain is used, water is flushed through the trap and the water in the P-trap is replaced with new water, while the old water is flushed out the drain.
  • Over a period of time, solids will stick to the trap and may lead to a clog and the trap may need to be cleaned or replaced.

Good to know!

P-traps are relatively inexpensive and can be replaced by DIY plumbers in about an hour or by a professional in about 20 minutes.

Plumbing drains: moving wastewater out of the house

Drains are an integral part of any plumbing system. These are the pipes, usually hidden under a sink, bathtub, shower and appliances that take the wastewater out of our house and (hopefully) out of our lives.

Drainpipes can be made from a variety of materials. As local building codes regulating the materials in drainpipes have changed over the years, an older home may have one or a combination of the following:

  • PVC: This material tends to be the standard in home drainage pipes. It is typically a white, rigid plastic that is strong, chemical resistant and easy for the homeowner to cut, fix and replace. It also doesn't clog easily and is more affordable than other materials.
  •  Cast iron: Usually used on large diameter pipes, this material is heavy and effectively deadens the sound of running water. A cast-iron drainage pipe is strong and durable, but it's not easy to cut. It's used for main sanitary waste lines and vent pipes in older homes.
  • Galvanized steel: In an older home, you might come across galvanized steel. This material is strong, but is more likely to rust and corrode.
  •  Copper: In rare cases, drainpipes may be made of copper. But this material is more typically found in supply pipes.

Watch out!

Always check with your municipality or a professional plumber before changing the material of your drainpipes. Some materials, such as lead that used to be popular, are no longer permitted.

Understanding more about your home's drainage system and trap locations may make it easier for you to diagnose an issue, such as a blockage, and confidently tackle the repair. Armed with a little knowledge and some basic plumbing tools, troublesome traps and damaged drains are no match for your DIY abilities.

The material on this website is provided for entertainment, informational and educational purposes only and should never act as a substitute to the advice of an applicable professional. Use of this website is subject to our terms of use and privacy policy.
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