The Brew Cabin

The rainwater downpipe at the rear of my house discharges into a hole in the yard - possibly an old soakaway. I intend to install a trapped gulley and run a pipe to an adjacent foul inspection chamber (old, brick), break into it and re-bench. Are there any problems doing this? Alternatively I could saddle into the underground section of pipe from the bathroom/kitchen waste pipe, which then runs to the foul chamber. What do you reckon?

Connecting surface water to a foul system should only be done when there's no other alternative and you MUST use a trapped connection. This can be achieved by using a P-trap and Hopper arrangement, or by using a trapped gully.

Whether you break into the existing MH and re-bench it, or use a saddle is up to you. With older systems, trying to saddle-on inevitably ends up with loads of broken pipes and you have to dig up half the yard to replace all the cracked pipes and the broken collars. If you opt for a MH entry, you can always install a capped spur while you're at it, just in case you have any future drainage requirements.