Why Both Sides of a Double Sink Clog: A T Fitting Diverter

Both bowls of a double-bowl kitchen sink were clogging, and the cause turned out to be a small plastic part inside the T fitting. Plumbing and heating contractor Richard Trethewey works through the drain to find it.

Reading the symptoms

The disposer sits on the right-hand side, with a regular sink strainer on the other bowl. A complaint confined to the side with the disposer suggests it isn't grinding food well enough. Here both sinks were clogging, so he looks for potential choke points in the drain underneath.

Where a drain can choke

He names three places to check: the disposer discharge, which runs into a pair of fittings (one black, one white); the T fitting where the strainer connection meets the disposer connection; and the P-trap. The trap keeps sewer gas from coming back from the sewer pipe up into the building, using a small water seal, but it can clog. If none of these is the problem, the pipe that goes down to the basement may have to be opened and cleaned.

Finding the culprit

The elbow from the disposer looks fine. He then breaks the tail piece coming down from the sink, where something doesn't look right, and then checks the T fitting, which is gunked up at the top.

Inside a new T fitting, the opening has a piece of plastic in the way. This diverter lets water from the strainer connection come down, while water from the right-hand sink is sent downward so there is less chance of it splashing up in the left-hand bowl. The diverter also makes the opening smaller, which he calls a perfect place to create a stoppage.

The replacement

He prefers a full-size brass T fitting with no baffle, and that is what goes in. The elbow fitting gets a new gasket and a nut. The flange tail piece has a special top gasket that sits down inside, and a nut holds it to the underside of the strainer. He snugs the nuts with pliers and installs a plug in the bottom of the trap.

Testing

Paper towel goes underneath to reveal drips while water runs. He says the only real test is to put the stopper in the left-hand bowl, fill it and let it discharge all at once. There were no drips, and it was draining really fast.