How to connect a dishwasher and washing machine to one waste pipe

Dishwashers and washing machines are essential household appliances that help save time and energy. While they assist with daily chores, you can focus on organising your family life, household or career.

You might be in a situation where you want to install both appliances but there is only a wastewater outlet for one appliance. In this case, you would need to plumb in an extra wastewater outlet for the additional appliance to function and expel waste.

However, you might find yourself stuck if you don’t have the means, ability or access to plumb in a new washing machine or dishwasher and waste pipe feeding to the outside drain. If this sounds like you, the solution is to attach your washing machine, dishwasher or both to a combined waste outlet that stems from your sink waste.

This guide will explain the benefits and process of plumbing your dishwasher and washing machine into one waste pipe at the sink waste outlet.

Table of contents

What is a waste pipe?

Waste pipes take wastewater or “grey water” away from your home and funnel it to the outside drain. They take water away from sinks, baths and showers. However, they also drain wastewater away from washing machines and dishwashers.

What is a waste pipe?

How to install a washing machine and dishwasher

Installing washing machines and dishwashers are similar as they need three fundamental connections; an electrical power supply, a water inlet and a wastewater outlet. 

Electrical power supply

You can use a standard electrical socket in the wall for the electrical supply. 

Water inlet

You will also need a water supply for your washing machine and dishwasher. Your washing machine might need a hot and cold water supply, although most only need cold. Dishwashers only need a cold water inlet.

Wastewater outlet

MASTERFLOW 1.5m Washing Machine Drain Hose Grey

If you have a new washing machine or dishwasher, it will come with a flexible waste hose. The waste hose discharges wastewater from your appliances to the waste pipe, which needs to be above the top of the washing machine drum. If you need a replacement, we provide spare flexible drain hoses at Build & Plumb.

Your legal obligation is to ensure that any waste pipe you attach to the drain hose includes a P trap with a U bend between your sink or appliance and the mains drain. This is to prevent foul smells from coming from the drain into your home. 

If you have a new washing machine or dishwasher but no wastewater outlet connection; and want to avoid the hassle of plumbing in a new standpipe to feed the wastewater to your drain, you can always use a sink and appliance waste trap. These duel nozzle waste traps funnel the wastewater of your washing machine and dishwasher through your sink waste pipe and to the outside drain.

Benefits of one waste pipe

Using a twin nozzle wastewater outlet to join your sink, dishwasher and washing machine wastewater is a quick and easy solution to add an extra appliance to your kitchen or utility room. The twin nozzle waste trap is particularly helpful if you can’t drill holes in your exterior wall.

Furthermore, using an existing wastewater pipe eliminates the reason to have extra unsightly wastewater pipes leaving the exterior wall of your home. 

What tools do I need for the job?

To connect your washing machine and dishwasher waste pipe to an existing sink waste pipe system, you will need

MCALPINE 1½" Kitchen Sink Trap with Twin Nozzles for Washing Machine & Dishwasher - WM11

Where should I position my appliances?

Before replumbing your dishwasher and washing machine waste pipes, ensure your appliances are in the right place first. Place your dishwasher and washing machine on a firm, level floor or use a spirit level and adjust the feet to make the appliance level to prevent excessive vibrations. 

Place your appliances close to your sink to prevent using excessive extension drain hoses or extra pipes. Having longer hoses or hose extensions comes with the risk of sagging waste pipes, which can cause water to stagnate in the pipes.

Benefits of one waste pipe

How to connect a dishwasher and washing machine to one waste pipe

Once you have all your equipment and you have your dishwasher and washing machine ready, it’s time to replumb your sink waste pipe.

  1. Firstly, you need to prepare your area. Take out anything that you store under your sink. Then, lay down your towels and place a bucket underneath your sink waste pipe, as there will be water sitting in the pipe, and there could be messy sludge.
  2. Disconnect your old waste pipe trap by unscrewing the two compression nuts. Then, pull the old waste pipe trap away. 
  3. Now, get ready to attach the Kitchen Sink Twin Nozzle Trap for Washing Machine and Dishwasher by unscrewing the compression nuts. Remove the washers and seals and place the new waste trap over the connecting pipes. Ensure the new waste trap is in place, the connecting waste pipes are pushed right down to the collars and move the washers and seals into place. Then screw the screw-up caps tightly. 
  4. Run the cold tap for a few seconds to check that there are no leaks.
  5. Now, connect the appliance drain hoses to the nozzles on the sink waste trap. Take the drain hose ends and attach them to the nozzles. Shimmy them up the nozzle as far as they will go. Lastly, tightly secure them with jubilee clips. 


It is possible to connect your dishwasher and washing machine to one waste pipe under your sink; often, it is the better and more efficient option. Why not look at our waste pipes and traps to suit every plumbing situation and find the best one for you? And for more washing machine and dishwasher spare parts, browse our collection online today.

Here at Build & Plumb, we want to supply you with the knowledge and tools to complete all your DIY and plumbing projects at home. Why not browse our essential plumbing tools to prepare for any at-home plumbing issues? 

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