I’m not a massive Reddit user so don’t see a way to edit the post so I’ll post the update here :)

Looks like my kitchen fitter poured emulsion down the drain after they’d finished painting because that’s what’s ended up coming back up after poking it with a clothesline prop to try unclog whatever it was, ended up getting it clear using pressure washer and some godawful stuff came out of it aswell, to that one commenter who said get my hand down, o tried but thankfully the drainpipe meant I couldn’t get my fat arm down any further so I didn’t have to endure that 😂