Step 4 · Install Vent Lines
Every drain trap needs a vent to function. Extend the drain pipes vertically up into the wall cavities after the trap for each fixture. The sink drain arm (stub-out) will typically be 18-20 inches off the finished floor. Above the sanitary tee for the sink drain, a 1.5-inch or 2-inch pipe continues upward as the vent. The shower and toilet also need to be vented. Often, you can tie all the new bathroom vents together in the wall or ceiling into a single, larger vent pipe (e.g., 2-inch). This main vent line must then be connected to your home's existing main vent stack or, if that's not feasible, run independently up through the roof. Use a drill with hole saw or auger bits to run the pipes through wall studs and ceiling joists. Secure the pipes with pipe straps. Code dictates the maximum distance a fixture's trap can be from its vent, so consult your local code.