Kitchen Sink and Faucet Swap: Removal, Disposer and Drain Hookup

Before swapping a kitchen sink in Colorado, Richard Trethewey of Ask This Old House found something he had not seen before: two separate traps under the old sink, one for the sink and disposer and another for the dishwasher, joined by a standpipe with an air gap. He was told that in this jurisdiction it was once code, meant to keep contaminated water from the disposer from getting back into the dishwasher. It is no longer code, and he removed it.

Why the old drain setup came out

Trethewey names two problems with the standpipe arrangement. If the trap ever clogged, dishwasher water could overflow the standpipe and flood the cabinet instead of going into the sink. And if the dishwasher was not used enough, the water in its trap could evaporate and let sewer gas into the building.

He cut off the dishwasher trap, left part of the fitting's shoulder so it matched the cap he had, put the cap on and tightened a stainless steel clamp. The dishwasher discharge now runs into the disposer, which has a tapping made for it. A special adapter fits that tapping on one side and the hose on the other, secured with stainless steel clamps. He ran the dishwasher hose as high as he could inside the cabinet to rule out backflow from the disposer.

Removing the old sink

He disconnected the water, loosened the drain nut so the sink could rise, and released a series of clips under the countertop. Because the countertop is laminate and the rim might have adhesive beneath it, he ran a putty knife around the edge before lifting. He unplugged the disposer's electrical connection, and he and the homeowner, Christy, lifted the sink straight up.

The new sink and faucet

The replacement is a standard 33 by 22 inch stainless steel double bowl, so it fits the opening and keeps the disposal on the left. Metal thickness is given as gauge: the lower the number, the heavier the metal. Stainless sinks come in 22, 20 and 18, and this is 18. A gasket is built into the underside of the rim, so no bead of silicone is needed, and the clips come factory mounted. It has a single faucet hole.

The faucet's spray hose is part of the spout. Trethewey installed it on the sink before setting the sink in place. The manufacturer's special wrench tightens the last bit, and a weight on the stainless flex hose helps retract the spray hose. A clip holds the watertight hose-to-faucet connection.

Setting the sink and connecting the plumbing

The sink was lifted high enough to connect the water supplies, then lowered into place. The clips flip down and are tightened with a screwdriver. Hot and cold (red and blue) connect to the shutoff valves with compression connections.

For the disposer, putty is rolled into a snake and set around the throat piece. Two adapters go onto the throat, a lock ring snaps into the groove, and tightening the screws squeezes out the putty for a tight seal. The other bowl's basket strainer uses a gasket, a bell-shaped flange and a nut tightened with pliers. Excess putty is scraped off and returned to the container.

The disposer has a knockout plug for the dishwasher connection, which must be knocked out first. The disposer locks to the sink adapter with a lock ring turned a bit more than a quarter turn, using a screwdriver for leverage.

The drain

Trethewey reused as many old pieces as possible. These are compression connections, with a nut and a gasket. A top gasket joins the straight piece to the basket strainer, and a tee fitting runs to the disposer. A piece that was slightly too long was marked and cut with a special pipe cutter rather than a hacksaw. On the disposer, a yoke with two screws compresses the gasket.

With power and water back on, Christy tested the faucet and the spray, and there were no leaks.