ᐅ Looking for a suitable adapter to connect a metal downpipe to a PVC drain pipe (commonly known as a sewer pipe or underground drain pipe).

Hello everyone,

I am looking for a proper solution to connect my downspout to the existing wastewater pipes.

The downspout is made of a dark metal sheet and has an inner diameter of 77mm (3 inches), outer diameter 78mm (3.1 inches). I am not sure about the material, it could be copper.
A suitable fitting needs to be found so that it can connect to the existing DN110 (nominal diameter 110mm / 4.3 inches) sewer pipe (also known as a "10 pipe").

Image attached.

What I find mostly does not fit well. Usually, it is way too large.

That is a 76mm (3 inch) downpipe diameter if you measured correctly; it appears larger in your photo. A 76mm (3 inch) downpipe fits into a 70mm (3 inch) soil pipe socket, then you only need a 70/100mm (3/4 inch) adapter piece.

What is it exactly? It looks like a repurposed rainwater pipe flap. Does it come out of the wall or from above?

Thank you for your response. This is simply a downpipe coming from the gutter at the top. Originally, it extended all the way down into the stoneware pipes. The orange KG pipe is now inside the stoneware pipe. It was planned to connect additional drains there (a second downpipe, light well, possibly even a rainwater harvesting tank in the future, but not for now), so it was replaced with the KG pipe.

The flap is still attached, as you can see in the picture. Originally, it led into a rain barrel. Maybe it will again in the future, we’ll see.

Yes, it could also be 76 mm (3 inches), but I don’t think the exact millimeter matters as long as it fits into a rubber seal.

As far as I know, HT pipe is not suitable for outdoor use, or am I mistaken?

Yes, that's correct, HT is not suitable for outdoor use, that just slipped out.

70mm (2.8 inches) with socket remains the same.

I just remeasured and this time I’m quite sure it’s 79mm (3 inches). I verified it several times.
So I will need a transition fitting from 80mm (3 inches) to 100mm (4 inches).
I’ve seen that these are available in zinc or copper. Then the sewer pipe can connect directly below.
In theory...

First of all, the dark downpipe with the nice rainwater flap is a copper pipe. It never breaks, but you can only connect it with a copper pipe. At least, you should do that.

I would shorten the KG pipe and install a suitable section of copper downpipe. Of course, there are also adapters from copper pipe to KG pipe. The wall clamps are available as well.