A sanitary tee is a plumbing fixture that allows liquids to drain while also allowing the plumbing system to vent. The fitting resembles a normal tee fitting; the sanitary tee, however, when viewed from the side will have a definite downward sweep to the center inlet. This down-swept feature molded into the tee assists the liquid in its travels toward a drain pipe. The uppermost fitting of the tee is connected into the building's plumbing ventilation system.
Poly-vinyl chloride (PVC) plumbing fixtures make plumbing much easier for most novice-plumbers than copper or black pipe. In many cases where a drain is being installed where previously there was not a drain, it is necessary not only to install the drain, but also to install a venting system for the drain. The sanitary tee makes adding a venting method very easy. By adding the sanitary tee into the drain line, the vent can be plumbed directly off of the top of the tee, making the entire procedure hassle proof.
When plumbing a vent line off of a sanitary tee, it is imperative that the vent does not attach below any other drain. This could make it possible to drain sewage or liquids through the tee and even send it back into another fixture, such as a sink. All PVC pipes running up from vent systems must merge above all drains in the structure and then be vented into the atmosphere through the roof.
The curved center section of the sanitary tee discourages siphoning from sink traps and drains when installed properly. Improper installation of the fitting could lead to draining difficulties for the drain system it is installed in. One sign of an improperly functioning tee is a gurgling and chugging action from the drain that is running into the tee. A plugged vent gives the effect of pouring milk from a jug. Without proper air flow and ventilation, the milk chugs in starts and stops while leaving the jug.
Sanitary tees should not be used in place of drain traps. The trap is an important fixture in the plumbing system. It prevents gases from the sewer system from entering the structure from the sink drain. The tee simply assists the drainage from exiting the sink and venting any gas or odor through the ventilation system. It is important to assure a proper seal of any joint when assembling a venting system. Steam, condensation and even rainwater can find a way into the vent pipe. A poor seal at any junction can lead to damaged ceilings and walls.