|Posted on June 10, 2015 at 8:00 PM|
Plumbing an island sink is challenging. It can't be vented the same way as a regular kitchen sink. Here's how it works.
Plumbing vents (a network of pipes that carry air and gas outdoors through a pipe exiting your roof) are essential to supply enough air to keep equal pressure in the plumbing system. They keep water and waste moving through the pipes at the right speed. A flow that's too slow leaves behind debris that clogs pipes. If it's too fast, suction siphons water from the P-trap (see photo below), allowing harmful sewer gas to enter your home. A regular kitchen sink, adjacent to a wall, has a vent hidden in the wall that connects to the drain. So it won't plug up, the vent must rise 6 in. above the overflow level of the sink before the pipe goes horizontal. Obviously, a vent pipe in a kitchen island can't do that.
As an alternative, most plumbers recommend a special type of vent (photo below) that loops as high as it can go inside the cabinet before heading under the floor and over to the main vent in the wall. Always get approval from your local plumbing inspector before installing this type of vent. A second clean-out may be required in the vertical wall vent pipe.