I had a CCTV inspection done of the sewer and drains at the back of my house. I have attached a pic and a sketch if the layout. It was all pretty much as expected until he found an unexpected branch. Basically, there are two waste drains that connect into a sewer via a manhole in the garden. The main waste drain that comes from the upstairs bathroom has the unexpected branch coming from the right. The pipe is shown highlighted in orange and the guy had no idea where it was coming from..... but there is a constant trickle of water coming from it. The photo shows the two drains entering the sewer - the arrows show the flow. The green arrow is from the upstairs bathroom that has the unexpected branch in it. I turned my stop clock off and the water continued to flow. My neighbour also turned hers off, and this didn't make any difference. Anyone got an idea what it might be coming from?