Can I run grey water into a soil stack?

[Jaygray]

Two questions in one here.

I'm/my plumber are looking to add a bathroom where my preextension kitchen would have of been.

My plumber thinks it's best to get ground works done and add a new terminal to my external drain.

Probably the best option, but costly.

My soil stack is very close to the new bathroom but behind a double wall, inside our extended kitchen.

Question one: can I send my grey water: washing machine, shower and sink etc into my soil stack?

Question two: how easy/safe is it to drill through a double wall?

My sewage system collects both grey water and black in one. So I guess it's OK?

 

[Madrab]

a double wall

Do you just mean a cavity wall? If so then no issue to core through that.

My sewage system collects both grey water and black in one. So I guess it's OK?

As long as you are sure it's a combined sewer then yes the soil pipe could be used. You should be able to check that with your LABC though - changing existing room, to a bathroom requires planning I believe.