What is a Plumbing Trap?

Have you ever looked under your bathroom or kitchen sink and wondered why the pipe was an unusual U-shape? If you’re like most people, you didn’t think twice about it’s shape and just assumed it had to have some practical purpose. This weird-shaped pipe is a plumbing trap. It is designed to hold a small amount of water in order to seal the drain and keep sewer gasses from escaping the drain and entering your home. Every drain has a plumbing trap because any connection that leads to the drain system is also a possible outlet for sewer gas.

Some pretty nasty odors can come from sewage disposal systems, and some can even be dangerous. Methane, Hydrogen Sulfide, Nitrogen and Carbon Monoxide can all be produced in a sewage system. Barriers are placed between the plumbing fixture and the sewage waste system in order to protect us from these gases.

Types of Plumbing Traps


This type of plumbing trap is mostly used for under kitchen and bathroom sinks. It is used for an outlet through the wall. P-traps are more commonly used nowadays because it’s the safest version of a plumbing trap.


s-trapThis type of plumbing trap is mostly used for toilets. It is used for an outlet through the floor. S-traps have the tendency to easily dry out even when they’re well-vented, meaning they can’t keep gasses from entering a home. S-traps are now banned in a lot of new construction in the U.S.

Here at Boston Drain Company, we offer plumbing trap replacement, repair, realignment, cleaning, and annual maintenance and inspection! Contact us for a free estimate today! 617-265-8888

Posted in Frequently Asked Questions, Plumbing News, Sewer & Drain Blog.