Father in law was in hospital when builder did his extension and his wife agreed to everything he said.
The plan shows new drainage around the perimeter and associated inspection and rodding points.
None of this was done and everything ( shower, toilet, sink and rain water) were connected to the existing system which is now covered by the extension which is now complete.
Builder was sacked long ago, there was some legal advice and think my relative kept the final payment. He is 85.