Neighbour connecting soil pipe to mine?

[JLbaby]

My next door neighbour is in the process of renovating and wants to put a toilet upstairs like I have - terraced house so our toilets upstairs would back on to each other (main bathrooms are both downstairs). He has asked if he can connect his soil pipe to mine to avoid having to do the pipe work and drainage, I have no idea about plumbing or pipe work so no idea if this is a good idea or not, does anyone know?!

My instinct says no, as what happens if they block up their pipes, would that affect mine? I’m a bit clueless on this but don’t want to come across as Un-neighbourly as they seem really nice and don’t want to have any animosity. Any advice on this would be great, thank you!

If you want a polite excuse say that you have spoken to a solicitor friend who has told you that it would create legal problems if you sold.

You can't stop them using a macerator. The idea of a macerator is that the waste from the toilet can be fed into a narrow waste pipe (like the one under a basin) rather than the much wider one that usually runs off from your loo. The macerator units themselves, which are located immediately behind the loo, are notorious for blocking and getting jammed, especially by tampons. But this wouldn't really be your problem.

Thanks all, I’m going to say no and use the legal excuse. Knew I could rely on MN for wise answers.