Dishwasher Plumbing: How to Plumb In a Dishwasher

Plumbing in a dishwasher needs three things close to where it will stand: a water supply, somewhere to drain to, and a socket. If the kitchen already has them, fitting it takes minutes. If not, the work happens under the sink.

Short answer: Connect the inlet hose to a cold supply fitted with an appliance isolating valve, hand-tight with its rubber washer. Push the drain hose onto the spigot of the sink trap or into a standpipe, secure it with a clip, and route it up in a high loop under the worktop so dirty water cannot run back. Turn the valve on, run an empty cycle, and check every joint for drips.

1. The water supply

The inlet hose screws onto an appliance valve, usually a small tap with a blue or red lever on a branch from the cold pipe under the sink. If there is no branch, a tee is cut into the cold supply and a new valve fitted. Fit the hose hand-tight; overtightening squashes the washer and causes a slow drip.

Appliance valves give you a way to shut off the dishwasher without turning off the house. Water regulations also require every water system to prevent backflow, which is why connections are made with appliance valves and hoses supplied for the purpose, rather than improvised fittings.

2. The waste

There are two common ways to drain a dishwasher:

Into the sink trap. Many sink wastes have a spigot on the side of the trap for an appliance hose. On a new one, cut out the thin plastic disc inside the spigot first, or the dishwasher will not drain. Push the hose on fully and secure it with a hose clip.

Into a standpipe. A vertical pipe with its own trap, usually behind the appliance. Hook the drain hose into the top without pushing it far down, so there is an air gap.

Whichever you use, the drain hose needs to rise up under the worktop before it falls to the waste. That high loop stops water in the sink from siphoning back into the dishwasher, the most common cause of a smelly machine or dirty water left in the base.

3. The power

A dishwasher plugs into a socket, which should be in an adjacent cupboard where it can be reached without pulling the machine out. Do not run an extension lead behind the appliance. New sockets or circuits are an electrician’s job.

Mistakes that cause leaks

• A hose without its rubber washer, or with the washer twisted
• The membrane left in a new waste spigot
• A drain hose without a clip, which pushes off on the first pump-out
• A hose kinked when the machine is pushed back into its space
• A shared waste with one spigot capped badly

When to call someone

If there is no valve or spigot, or the pipes under the sink are old and crowded, new connections need cutting in neatly. Our appliance installation service fits dishwashers and washing machines, and our guide to installing kitchen sinks and appliances covers the wider kitchen layout.