Toilets not installed with a vent pipe or that have a clogged vent will not drain properly. The vent pipe supplies air to the drain line when the toilet flushes. This air prevents a vacuum from forming in the drain system. Indications of poor ventilation include gurgling noises when water drains and a drain that remains slow even after using a plunger or a plumbers snake. The vent pipe also allows odours and sewage gasses to escape the drain system. The toilet vent extends from the drain line up through the roof.
Place a PVC T fitting next to the toilet drain line in a spot where the vent pipe will have access to the roof. The vent usually runs through or next to a wall. The T fitting drain connections must match the existing toilet drain line size, either 75 to 100 mm (3 or 4 inches), and the vent connection on the T fitting must equal or exceed half the size of the drain line.
Mark the drain line with a pencil at the two spots where the T fitting female connections end. The female connections, found at the ends of the fitting, act as a sleeve around the drain pipe. The cut-out section will measure less than the total length of the T fitting, usually 50 mm (2 inches) less. Check the measurements with a tape measure.
Cut a hole in the roof where the vent will exit the house with a reciprocating saw. This hole should measure 25 mm (1 inch) larger than the diameter of the vent pipe. If the vent will run through a wall, then cut a section of the wall plates, or the boards the wall studs connect to, for the vent to run through.
Cut the drain pipe with a reciprocating saw at the pencil marks. Keep the cuts square to the pipe.
Clean the ends of the drain pipe and the female connections of the T fitting with PVC primer. A brush comes connected to the cap of the primer can.
Apply glue to the drain pipes and the two female connections of the T fitting that connect to the drain line. A brush comes attached to the cap of the glue can.
Slide the T fitting onto the drain pipe with a twisting motion. The final position of the vent connection of the T fitting should aim toward the roof.
Clean the end of the vent pipe with PVC primer.
Apply PVC glue to the vent pipe and the female connection of the T fitting. Slide the pipe into the fitting using a twisting motion. If a single piece of pipe extends through the roof, slide the pipe through the hole first, then push the pipe into the fitting. Pipes that do not reach the roof need a coupling primed and glued between an extension piece of pipe and the one that connects to the T fitting.
Secure the vent pipe to the wall and roof trusses with hanging straps every 150 cm (5 feet).
Cut the vent pipe 30 cm (1 foot) above the roof with a reciprocating saw. Slide a lead roof boot over the cut end of the vent pipe. Fold the end of the boot into the vent pipe. Secure and waterproof the lead boot to the roof with the existing shingles and roofing tar.
Follow all local codes when modifying the plumbing system.