Ben R wrote:
Hi

Thanks for all your advice. We have a septic tank and I was pretty
sure that the drain went into the tank - however, I will double check
as I don't want to drain it away anywhere else. Is it very unusual for
top water AND foul water to go to the septic tank?

To make absolutely sure I could run the outflow to the drain from the
kitchen (sink/dishwasher - on the presumption that this WILL go to the
septic tank). However, I would still be faced with the same problem. I
cannot run the outflow above ground to the top of a gulley because it
crosses a path around the house. Would I therefore have to extend the
drain?

As TNP has commented, very very unlikely! It could just be worth putting
in some drain tracing dye in to find out where it goes.