What is a wet vent? How do you vent tubs and showers?
A wet vent is a vent that is also used as a drain. Maximum trap arm length is 10' for a toilet to the vent and a sink and tub or shower is 5' from the vent.
The wet vent as shown on the drawing drains the sink as well as acts as a vent for the tub or shower.
The vent off the sink, tub or shower may also return to the main vent as an option to have only one pipe protruding through the roof.
Usually the drain stack is below the toilet and close to it, with a cleanout on the bottom.
Toilet drains are 3", sinks and tubs are 1 1/2" and showers are 2". A tee is allowed for a vent connection but only Y's are allowed for drains.
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