What Is The U-Shaped Pipe Under My Sink

Ever wondered why your drain pipe below the kitchen and bathroom sink doesn’t just go straight down into the floor, or why it has a U-shape? That section of your drainpipe is known as a trap, and it’s a critical part of your waste water disposal system. Without it, sewer gasses would come right back up through your sink drains and waft through your house.

The plumbing trap has two major purposes:

• To prevent sewer gasses from entering your living space. The pipe bend known as the trap ensures that there is a water seal separating the sewage system from the inside of your home. Like the rest of the wastewater system, it relies on gravity to keep the water within the bend. Whether you have a septic tank or a municipal waste management system, the organic waste creates fumes and gasses that can be foul if they enter your home. If the goal of the wastewater aspect of your plumbing is to isolate the organic waste from the homeowner, then the trap below the sink is a vital aspect of that.

• To prevent foreign objects from blocking up your entire plumbing system. Imagine that your sink drain on the second floor of your home were a straight shot down to ground level. If you’ve ever dropped a ring, toy, or some other foreign object in a drain, you’re probably glad to have that trap there. It prevents small blockages to become major ones.

Before it became U-shaped (or P-shaped as many refer to them), the trap was S-shaped. Its design allows water to pass through, while retaining a seal against the rise of foul odors, but when a drain is not used for some time, the water in the trap can dry out. If you have foul odors rising through your drains, there might be something wrong with your sink trap.