Have you had a new boiler installed or doing some renovating and want to tidy up your pipework? The condensate pipe is one of those pipes that can be connected to a waste pipe inside your home to save on having another pesky pipe on the wall outside. The process of connecting a condensate pipe to a waste pipe is actually quite simple. If you know what you are doing, it should take no more than around 20 minutes to complete the job. Before we get started on how to connect your condensate to your waste pipe, there are a few things that you need to know. In this article, we will cover what a condensate pipe is, what it does and whether you can connect your condensate pipe to your waste pipe under your sink.

Condensate pipe clamp

What is a Condensate Pipe?

Boilers, which are used to provide heating and hot water for homes, produce wastewater as a by-product. This is usually drained out of the system through what’s called a condensate pipe. This small plastic tube will exit from behind your boiler to an external wall which then connects to the sewer or septic tank in order to safely drain the waste!

Why Connect Condensate Pipe to Waste Pipe?

There are a couple of good reasons to connect your condensate pipe to your waste pipe.

  • Firstly, it will look tidier. If you are able to connect your condensate pipe to a waste pipe under your sink or somewhere else out of sight, it will be one less pipe attached to the outside of your house going into the drains.
  • Secondly, the weather. External condensate pipes are known for freezing over during the colder months of winter. This can be down to a few different reasons but most often, it is because the external pipe is extremely thin and not insulated.

How to Connect a Condensate Pipe to a Waste Pipe?

If you want to connect your condensate pipe to your waste pipe it is easy enough to do without the help of a plumber but if after reading this you are unsure, maybe you should give your local plumber a call to help you out.

What You Need

To tap your condensate pipe into an existing waste pipe, there are a couple of things that you will need and then the job will be a breeze.

Step 1 – Turn the Boiler Off

Firstly, you will want to turn the boiler off. Depending on what waste pipe you are tapping into, you may want to turn the water off too so that nobody runs a tap whilst you are working… it happens!

Step 2 – Locate the Waste Pipe You Want to Tap Into

Next up, you will want to locate the waste pipe that you want to tap into. Although your boiler will already have a condensate trap to prevent foul smells and gasses from entering your home, you still want to make sure that you install your connection after the trap on that particular waste pipe.

Note: Waste pipe clamps will fit 32mm & 40mm waste pipes.

Step 3 – Cut into Waste Pipe

Using your hole saw, cut a 15mm hole into the waste pipe (on the side or on the top). This step is extremely important so if you do not have one, make sure you buy the right attachment for your drill so you can cut a perfect 15mm circle.

Step 4 – Attach Condensate Pipe Clamp

This part is easy enough, the clamp will be in 2 parts. One part will have the washer attached that will fit nicely around the 15mm hole that you made. The other section can be attached by using the bolts provided therefore clamping the pipe. The clamp is 40mm but if you are clamping onto a 32mm pipe, the clamp has inserts so you can clamp to 32mm too.

Step 5 – Attach Condensate Pipe to Clamp

The easy bit, now you can connect up your condensate pipe to your waste pipe for a nice clean finish.

Condensate Pipe Clamp Installation

How to Connect Condensate Pipe to Soil Stack

There are a couple of ways for you to tee into an existing soil stack. The first way is much the same as when tapping into an internal waste pipe. All you need is a strap boss connector and it works in much the same way as the condensate clamp. The other way is to get a soil stack branch fitting. Branch fittings just replace a small section of the soil stack and can take multiple waste pipes together.

Problems with Condensate Pipes When Connected to Waste Pipes

In the past, I have come across a couple of problems where people have connected their condensate pipe to a waste pipe unsuccessfully.


I have seen condensate pipes installed on the wrong side of the trap under a sink. Unfortunately, sinks and traps get blocked from time to time unless they are routinely cleaned (which most people do not do). If the condensate pipe is attached to the wrong side of the trap and the sink gets blocked, the condensate will just add to the problem.

This can cause problems with your boiler as they are designed to cut out if there is a problem with the condensate outlet.

Poor Join Location

I have also seen condensate pipes attached to the underside of the waste pipes without enough of an angle (fall) for gravity to do its job and let the water flow out. This was obviously a DIY job, but you must remember that water flows downhill!


As you can see, with the right tools and a little time you can connect your condensate pipe to your waste pipe with ease. We recommend that if you are not sure about your pipe layout and where is best to make the connection, you should probably call a plumber to come and assess the situation.

How to Connect a Condensate Pipe to a Waste Pipe Infographic

Plumbing Wizard Tips

“Same with any plumbing or pipework, if you are unsure, call a professional!”

“Water flows downhill, make sure that you have enough fall for gravity to do its job!”

“Installing the condensate pipe clamp is relatively foolproof – just ensure you cut the right size hole into the waste pipe!”

“If you are connecting your condensate pipe to the soil stack, wrap the external pipe in foam insulation to help prevent freezing!”

Frequently Asked Questions

Can a condensate pipe go into a waste pipe?

Yes, a condensate pipe can be routed into a waste pipe. This is best done after the trap on the waste pipe in case of blockages.

How do I connect condensate pipe to waste pipe?

The best way to connect a condensate pipe to a waste pipe is to use a condensate pipe clamp. This clamp is designed specifically for this purpose and can be used on 32mm and 40mm pipes.

Where does a condensate pipe go?

The condensate pipe is part of your wastewater system that should be routed into the sewer system. The best way to do this is to tee the condensate pipe directly into a waste pipe.


Lee Pearce is not just a master plumber; he’s a veritable Plumbing Wizard. With over 30 years of experience in the trenches of pipes and drains, Lee has become the go-to sage for DIY plumbing, saving homeowners thousands in potential call-out charges. As the founder of Plumbing Wizard, he’s dedicated to demystifying the complexities of home plumbing, offering easy-to-follow advice that stands the test of time and pressure. His online blog is a treasure trove of tips, tricks, and tutorials that empower everyday individuals to take charge of their home’s plumbing health. Lee’s practical wisdom is not just about fixing leaks; it’s about imparting confidence and self-reliance. When he’s not writing or elbow-deep in a plumbing project, Lee is passionate about educating the next generation of DIYers, ensuring that practical skills are passed down and preserved.

More You Might Like