The carpenters I work around prefer I don't drill 2" or 2 1/4" holes in a 2 x 8 floor joist. I can get away with one or two maybe, but they have to be close to the center of the joist, not in the top or bottom 25%. Usually doesn't leave much room for grade so I generally run them below the joists, next to the closest wall. Leaving a few extra cleanouts along the way, as needed. If I were you I would investigate this "grey water well",maybe it would be quicker, cheaper, faster just to increase the size of it and the pipe leading to it.....Lou

• Lou's Plumbing/Gasfitting