I recently got a plumber to do some work on my cast iron soil pipe. He
used some kind of thick, black, soft, sticky tar to seal the connection
between a 40mm waste pipe and the (slightly larger) boss pipe on the
soil stack.

Can anybody tell me exactly what this tar is, and where I can get some?
It's definitely not Plumbers Mait! For unforeseen reasons I need to
replace the waste pipe. I can pull it out of the tar easily enough, but
I will need some more to reseal the gap around the new length of pipe.

Vaci