#14054

Give it a go, you never know your luck. But if you aren’t allowed to core to the outside, you could try this:

Forget the dry waste idea. Instead, you could create the floor waste by raising your floor level (if your ceiling height allows). You can run your waste pipe into the kitchen stack (this is an internal pipe). 

If you can imagine, you’ll be stepping up into your new bathroom and the pipework will sit under that floor.

Your waste pipe from your kitchen sink will tell you where the stack is.