Plumbing drains require proper ventilation, typically through pipes that extend to the roof to allow air into the drain lines to equalize the pressure and allow grey water to drain. In some instances, such as a kitchen sink that was improperly vented when first installed, running a new vent line to the roof might not be feasible. For these cases, you may install an in-line vent in a kitchen sink utilizing a one-way valve, called a mini vent, that allows air into the line but never back out.
Clean out the cabinet beneath the kitchen sink. Put a towel directly beneath the drain line. Loosen the couplers and eliminate the P-trap and tailpiece from the sink drain line.
Cut a 3-inch section of 1 1/2-inch PVC pipe, then using a PVC cutter along with a hacksaw. Implement PVC primer to a end of this 3-inch section and to the interior of the drain coupler in the wall beneath the sink. Implement PVC glue across the primed portion of this 3-inch piece and add it halfway into the coupler.
Prime the exposed stub of this installed 3-inch piece of PVC in addition to the lower coupler of a 1 1/2-inch wye connector. Place the PVC across the stub and attach the wye to the stub. Verify the lead-in coupler of the wye is pointing upward toward the sink basin.
Measure the distance between the wye lead-in coupler and the bottom of the sink. Subtract 4 ins from this space. Cut a section of 1 1/2-inch PVC to this span. Prime and connect a 1 1/2-inch threaded feminine PVC coupler to a single end of this section of PVC.
Thread a mini vent into the threaded female coupler and tighten the vent to the coupler as firmly as you can, using your own hand. Prime the opposite end of this section of PVC to that the vent is attached, in addition to the very best coupler of the wye beneath the sink. Apply glue to the end of this primed section of PVC and put in this vent tube into the coupler on top of the wye.
Thread the sink tailpiece to the bottom of the sink and then hand-tighten that the coupler. Dry-fit the sink trap involving the bottom end of the tailpiece and the open end of the wye connector. Cut the trap tube so the trap fits nicely between the tailpiece and the wye. Combine the tube between the tailpiece and the wye by massaging the couplers.
Turn on the tap and drain water through the sink drain while watching for leaks anywhere in the drain line beneath the sink. Remove the towel and then replace the contents of this sink cabinet.