In message , Crazy Dog
writes
I'm looking for a rainwater diverter for a 2-1/2" OD cast iron downpipe. All
I've found, so far, state either "suitable for PVC" or "not suitable for
cast iron."

Replacing the old downpipe would be a last resort.

Does anyone know of a supplier of a suitable diverter?

ISTR Rusty having an intriguing home-made system a couple of years ago?
--
June Hughes