There are several reasons why there is a trap under your sink, and if you are renovating your home, you should always make sure that one is installed in every room in your house where you have a faucet. This includes the kitchen, the bathroom, the utility room and anywhere that you may have plumbing . A P-Trap, which is sometimes called by plumbers as a Stink Trap or water trap is the "U" portion which makes your sink safe from incoming sewer gasses and anything else like vermin that might come into your home through the drain. This is accomplished by the water which rests in the "U" portion of the trap.
The fact of the matter is that without P-Traps in your home the smell would be unbearable. not to mention dangerous, sewer gases contain all sorts of chemicals including methane which besides being explosive is deadly. Every year a plumber dies from inhaling methane while working on sewer piping, In fact it's sewer gas is so bad that a person entering a manhole must be attached by a harness so they can be lifted out incase they pass out.
P-Traps come in many materials , finishes and thicknesses a standard P-Trap under a sink is normally made out of brass tubing and is required to be of 17 gauge. A 17 gauge P-Trap is thicker and lasts longer than a 22 gauge P-Trap. At George Salet plumbing we only use 17 Gauge P-Traps for sinks. All plumbing fixtures have some type of P-Trap Bathtubs, Showers and floor drains all use P-traps to prevent gases from entering the living spaces these P-traps are made out of cast-iron, copper, Plastic and glass pipe. A toilet bowl acts as it's own P-Trap with the water in the bowl creating the water seal.
While it does seem like a simple plumbing device, if you are buying a home, always make sure that the P-Traps are in place. This will insure that your home or condo will not allow vermin or sewer gas to enter your home through the drains.