Dishwasher plumbing: supply, waste and the usual leaks

A dishwasher is usually plumbed in under or next to the kitchen sink, sharing its water supply and waste. Most of its plumbing is simpler than a washing machine's, but its drain arrangement matters more. Get it wrong and dirty sink water can find its way back into the machine.

If you are dealing with a washing machine instead, see washing machine plumbing.

The supply side

A dishwasher normally takes a single supply. Most machines are cold fill. Some can take hot. Check the manual before you connect it to anything other than cold.

The supply usually comes from one of these:

• An angled appliance valve on the cold pipe under the sink. Its outlet faces along the wall, so the hose does not stick out and get crushed when the machine is pushed back.
• An appliance tee valve, fitted into the cold pipe to the kitchen tap so one branch carries on to the tap and the other feeds the dishwasher.
• A self-cutting valve that clamps on to a pipe. These are less common in new installations. If you have one and it weeps, ask a plumber about replacing it with a compression valve.

Whichever you have, it should be easy to reach once the cupboard is empty. It is the valve you close before doing anything else. Our isolation valves guide explains the types.

The waste side

The drain hose carries dirty water from the dishwasher's pump to the kitchen waste. There are two usual routes:

• A spigot on the sink trap. Many kitchen traps have a side nozzle for an appliance hose. The hose pushes on and is held with a hose clip.
• A waste spigot or tee in the waste pipe after the trap, often with a non-return valve built in.

Two details cause most problems:

1. The loop. The drain hose should rise up high under the worktop before it drops to the spigot. This loop helps stop sink water draining back into the machine and stops the machine emptying itself by siphoning. The dishwasher maker's installation sheet says how high it should be. Follow it.
2. The blank. New traps often come with the appliance spigot sealed off, so the trap works as a normal sink trap until something is connected. Wickes's listing for the McAlpine WM11, for example, says it "includes blank plugs". On some traps the blank has to be removed or cut out before the hose is fitted. If a newly connected dishwasher will not drain, check this first. If the sink itself is being replaced, see kitchen sink installs; if it has a food waste disposer, see waste disposal units.

If the sink gurgles or fills with dirty water when the dishwasher empties, the waste is probably partly blocked. Start with our blocked sink guide.

Before you pull the dishwasher out

Integrated dishwashers are usually fixed to the worktop or the cabinet sides with small brackets, and the kicker board may need removing. Then:

1. Switch the machine off and unplug it, with dry hands and a dry floor.
2. Close the appliance valve.
3. Put a towel and a shallow tray under the sink. The fill hose and drain hose will both hold some water.
4. Ease the machine out slowly, feeding the hoses and power cable through the cabinet so they do not snag.

If water has reached the plug or socket, do not touch them. Switch the electricity off at the main switch only if you can reach it from a dry place. Otherwise keep away and call an electrician.

Where dishwashers leak

Under the sink, at the valve. Usually the hose washer at the valve outlet. Close the valve, fit a new washer and refit the hose by hand.

At the drain spigot. A missing or loose hose clip, or a hose that has slipped half off. Refit and clip it.

Out of the trap. A trap nut has loosened, or the seal has moved after the hose was pushed on. Reseat the trap nut by hand.

At the front of the machine or under it. This is often the door seal, overloading or the wrong detergent causing foam, or a fault inside the machine. Check the filter and spray arms as the manual describes. Anything inside the casing is an appliance repair for the maker or a qualified appliance engineer.

Some machines have a flood-protection hose with a valve at the tap end, and a float switch in the base. If the machine shows a leak or flood error, unplug it and follow the maker's instructions. Do not keep resetting it.

Hard water and salt

In hard water areas, dishwashers use dishwasher salt to soften their own water internally, and a hardness setting on the machine. This salt is not the same as table salt or water softener tablets. Use the dishwasher salt the maker specifies. See limescale for scale more generally.

Parts at Wickes

We haven't tested this. Figures are as the maker states them (checked 13 November 2026).

Why does my dishwasher have dirty water in the bottom?

A little water in the sump is normal. More than that usually means it is not draining: a blocked filter, a blocked sink waste, a kinked drain hose or, on a new installation, a spigot blank that was never removed.

Can the dishwasher share the washing machine's waste?

Often, yes. Twin-nozzle traps and standpipe connectors are made for this. Each appliance still needs its drain hose arranged as its maker describes, so neither siphons or backs up into the other.

Do I need a separate valve for the dishwasher?

It is good practice to have one, so you can turn off the dishwasher without turning off the kitchen tap or the whole house. An appliance tee valve or an angled appliance valve is the usual way.