Here we have different pipes for Storm water and sewerage. 100mm nice and strong pipes for sewerage and 90mm very weak for storm water. However many people use 100mm for both after having the 90mm stuff break on them.
Connecting the roof to the sewerage is illegal as it overflows the treatment works when it rains. I have never seen it but been told very now and then they will pump smoke from the sewerage system looking for smoke from the roof to find houses with the storm water connected to the sewerage system.
