BTW, the road goes on forever and the party never ends ...
THere was 3' of drop in the pipe over the last 25'. I've been told a 4" pipe needs 1/8" per foot, so that's about 12 times as steep as it needed to be. I replaced that end, raising the end up so it's about an inch above grade there. So far so good, right?
Next we went to hosing the pipes out (had already spent days snaking them) and noticed that water crosses from the septic side over to the storm water side. So apparently I've got coincident crushing of both pipes, so water can cross from one to the other. Crazy right? I know it's underground and not something cross-plumbed in the house because we were shooting water in out past the slab, so the in-house plumbing isn't involved in the problem.
I'm still trying to avoid digging up the whole yard, so I finally chased down a rental place here with a see-snake, but it's about $300 per day, which is about the same rate as an excavator. I knew it was going to be expensive when the guy started apologizing as soon as I asked the price. I think it might be a worthwhile expense though, because then I could check out every pipe in the house, even back under the slab.