A strap Boss is only for 40mm pipe, rainwater pipe comes in 65mm how else can they be connected?

Most city codes will not allow rain downspouting to be connected to the sewer systems.

The debris flowing through a downspout doesn't break down and clogs the sewer with things like leaves building up till it needs vacuumed out.

I am not sure if this is any help.

KBC

I agree, I think that things should be arranged so no water leaves any lot. Putting extra water in the sewer system increases the load on the treatment plant and costs a lot to treat water that does not need it.

Good luck Roger

Sorry Bazzer, both posts are 100% right on. Should not do this but ask your city sewer department to be certain.