Before you get started

Always make sure the water supply is turned off before plumbing in a dishwasher or washing machine.

Dishwashers and washing machines are plumbed in using similar techniques. The information contained in this leaflet will be appropriate for plumbing in either appliance.

Supply pipes for dishwashers and washing machines are normally recognised by their red and blue tap sections on a simple isolation valve. If you do not have these valves, you must have some fitted.

Some appliances only need a cold water feed, so only one blue hose is required. All you need to do is follow the colour coding of the appliance you have bought. If the appliance does not have a red, hot water supply socket, a red hose supply is not required.

When directing a waste pipe, there are two options for where a pipe from a washing machine or dishwasher should go: either into the trap (U-bend) below a sink using an adaptor, or directly into the waste pipe through an 'upstand' section of pipe. This leaflet shows connecting to an adaptor on the trap. If you have a direct upstand system waste pipe, you simply need to push the appliance waste pipe hose sufficiently into the open end of the upstand. Some manufacturers have a bracket to hold the pipe curved in position. Some water authorities insist on this type of set up.

Both a washing machine and dishwasher may be fed into the waste assembly under a sink using two adaptors. However, avoid having both appliances on at the same time as it is best not to have both discharging into the waste assembly simultaneously.

If the supply pipe connections for the water are outside the unit that is enclosing the appliance, cut access holes through the side of the unit so that the supply pipes may be threaded through. This is the same process as shown for the waste pipe in steps 3 and 4 overpage using a hole saw attachment on a drill/driver.

Check the instructions that come with the appliance as it may have a non-return valve fitted to prevent the possibility of the back siphonage of waste water. If your waste discharges into an upstand waste pipe, if there is an air gap (gap betwen discharge pipe and drain where it discharges outside), you do not need to fit a non-return valve. If you are discharging into the sink waste, a nonreturn valve should be fitted, or make sure the waste pipes loop higher than the sink overflow. Fit a hook to hold at the appropriate height if necessary.

Plumb a dishwasher or washing machine


Make sure water supplies are turned off. Remove the stop end from the adaptor point on trap. You may have an adaptor point in place already.


Then simply screw the adaptor in place firmly, but do not overtighten.


Unless there is easy access, you will need to cut a hole in the side of the unit larger than the appliance waste pipe diameter. Attach a hole saw to a drill/driver.


Thread the appliance waste pipe through the hole and to the adapter on the trap assembly beneath the sink.


Position a hose clip over the adaptor on the waste pipe. Undo it sufficiently so it will be able to fit over the appliance waste pipe.


Push the appliance waste pipe onto the adaptor as far as it will go. Twisting slightly as you push will always help to achieve a solid connection.


Move the hose clip over the appliance waste pipe end and tighten using a slot-head screwdriver to secure the connection and ensure no leakage.


For supply pipes, check your machine to see if it requires just a cold supply or both hot and cold. This will vary between models.


Check that the washer is correctly positioned in the threaded connector before screwing in place on the back of the machine.


Ensure you do not cross thread the connection, otherwise it will leak. Always begin twisting the connector on by hand.


Gently tighten both connections with some water pump pliers. Do not overtighten as this will damage the thread of the connector.


Turn on the isolation valve(s) and check for leaks. Most leaks occur because of the washer in the connector. This is simple to change if necessary.