Dry Traps

• The trap is a curving piece of pipe that sits below a plumbing fixture. The curvature of a trap actually keeps water in it at all times, as long as you run water down the drain pipe regularly enough. The humidity will help determine how quickly the water in the trap will evaporate. A pet that likes to drink out of a toilet also will drain a toilet's trap. Once the trap is dry, sewer gasses can pass through, causing the plumbing to smell.
  
  

Vent Pipe Obstructions

• Every plumbing fixture is connected to a vent pipe, which replaces air that is lost when you wash water down a drain. When a vent pipe becomes clogged, the water level in different plumbing fixtures may change because of the lack of outside air being introduced to the plumbing. Without the proper amount of water in the plumbing fixture, the trap may not be full and sewer gasses will leak out. A plumber can look over your vent pipes, finding and removing clogs as well as any breaks in the pipes.
  
  

Bio Slime

• As you use your shower or a sink, you wash down organic materials, such as soap, hair and skin oils. Some of these materials stick to the sides of the drain, where they build up over time. The buildup results in a bio slime that is a breeding ground for smelly bacteria. Once the bio slime has formed, you must remove it with hot water, soap and a large bottle brush. Periodic cleaning of your drains will help keep the amount of bio slime down and avoid their odors.
  
  

Leaks

• A leaking pipe, especially one that is below a plumbing fixture's trap, will allow sewer gasses to leak out into your house. Leaks may be hard to pinpoint since the water can travel down a pipe for a distance before finally dripping off the pipe. A plumber not only will be able to determine the exact location of the leak, but also patch the pipe or replace it with a new section of pipe, correcting the problem.
  
  

Toilet Seal

• Each toilet has a wax seal that sits between the flange piece, which anchors the toilet's bolts to the floor, and the bottom of the toilet. When you install the toilet, you must compress the wax ring so it creates a watertight seal and prevents water from leaking out of the base of the toilet, as well as sewer gasses from coming into the house. If the wax rink breaks, you must remove the toilet and the old wax ring, and then install a new wax ring before replacing the toilet.