I went to a minor repair job today where the fitting below the valve had loosened up. I had replaced the old AS valves last fall with RB ASVFs, but I didn't go but a few inches underground and connected to the existng pipes. Checked it out today and there was a loose ell. Looked carefully after digging and bailing and found black glue residue in the socket and on the end of the lateral. Seems obvious somebody must have used the wrong glue... this was black, not gray... maybe an ABS glue? Anyway, cleaned and re-glued with purple primer and blue glue. Everything tested fine after 20 minutes.