Wastewater terrace roofing - 80mm by 75mm

Last year we got a terrace roof. Now I would like to channel the wastewater into our soakaway. In one post of the roofing is a PVC pipe from the company DYKA; at the end of the post, an 87° bend, also from the company DYKA, is glued to the PVC pipe. The inner diameter is 80mm. Unfortunately, I cannot find any PVC pipes and PVC bends in 80mm. Apparently, this is a Dutch size. Is there an adapter from 80mm to 75mm so that I can use an HT pipe and later a KG pipe? Or does anyone have a source for the DYKA 80mm PVC pipes and bends? Thank you very much!

I hope you mean rainwater and do not have a toilet on your terrace. In any case, I would never, ever, ever direct wastewater into the cistern.

(SCNR).

There is on the internet a: Zink Reduzierstück Fallrohr reduction d= 80/76mm or transition to HT 75mm, would possibly try it with that.