Advice for replacing down pipe

[Groppo91]

Hi I have attached some images of the current pipe which is cast iron and always getting blocked. It serves as the waste pipe for bath and sink, I have tried to flush it out with a jet wash but it failed to break through what ever is stuck.

I am happy to go ahead and replace it but would like some advice. What size pipe would I need and hopper?

Alternatively there is a soil pipe about 2-3meters over to the right, would I be better adjusting the two waste pipes along the wall at a small decline and make a connection to that? It will probably look awful and I don't like the thought of longer runs for waste pipe?

 

[PETE 123]

If you think its blocked solid might be quicker to break it all out and put a length of rainwater pipe and a new hopper.

 

[Groppo91]

If you think its blocked solid might be quicker to break it all out and put a length of rainwater pipe and a new hopper.

Thank you, this is the route I plan to take but what downpipe should I need I see some are 110mm is that the one?