we have a single drainage point for grey water - that links all sink'shower drains - separate drain for boiler and obviously cassette for toilet - thought this was standard

Obviously an area of improvement since ours was built!

We have this on our Dutch 2008 Troll, must admit I thought it was standard and not a “mod”. Although we don’t have a boiler so obviously no drain for that.

Tip I saw somewhere is to put a short section of bicycle inner tube on the end of the waste pipe, which then feeds into the waste water carrier. Works much better than random bits of solid pipe