My friend Jim taught me these important truths about plumbing as well as various techniques. Sadly, while it flows downhill, if it can't, it backs up. In this case, the lowest drain is the laundry sink. I removed the trap and discovered the blockage wasn't there. (OK, technically I broke the existing trap because one of the nuts was frozen tight, and replaced it.)
So I bought a nifty 25' x 1/4" snake that attaches to a drill to ease the twisting that's necessary. However, there's no cleanout at the laundry sink. D'oh! (It goes from 1.5" or 2" galvanized pipe into a 4" clay pipe with cement to seal the junction.) Fortunately, I was able to get the snake in through the T at the basement wall. With some low speed turns from the drill, it snake went in fairly easily -- loosen the thumbscrew, push the snake in gently until it meets resistance, tighten the thumbscrew, turn with the drill, repeat. Unbeknownst to me, I'd reached about 23.5' on the snake. I loosened the thumbscrew to repeat, then watched in horror as the end of snake came out of the reel and whizzed down the pipe. D'oh!
I bought a 35' x 3/8" snake. This one has no reel, so I know how near the end I am, but it's harder to twist. I ran it as far as I could into the laundry drain pipe, but to no effect. Hmm. I did spend a perfectly lovely afternoon carrying buckets of, well, you know, from the drain over to the sewer. Fortunately there's a small manhole into the sewer on our property so I could dump it there; dumping it into a toilet would have (a) been smelly and potentially messy (b) futile, since it would just come back down to the laundry sink anyways.
So today I called a rooter company. I described the problem, the lack of a cleanout at the laundry sink, the access to the main cleanout under the house. They could come in the afternoon, but wasn't sure if they could do anything because their big rooter probably wouldn't fit. Then they called back later and said their small rooter wasn't working, so there was no point in coming. D'oh! So I tried running the 35' x 3/8" snake into the main cleanout. No joy, but the telling thing was that I pulled up a few small roots. Hmm. (Needless to say, none of this was particularly good for the tendinitis in my shoulder. Physical therapy starts next week.)
So I called Roto Rooter, and they said they could be there within 2 hours. Yay! But since I was just talking to a dispatcher, there was no one to describe the access issues to. So about 1.5 hours later a friendly plumber named Martin showed up. I took him into the basement and showed him the layout, and he immediately realized it would be a two man job (and told me it would cost more.) But we had to wait for another plumber to show up first. In the mean time I took down the saw horses and table I had set up for the tile saw, and moved other things out of the way to clear the access.
45 minutes later, the other plumber showed up. They looked things over, debated about going down through the roof vent stack (I warned them the roof was not good to work on), but they ultimately decided they'd have to lug the machine down the hill after all. Then they tried to get the cleanout cover off. They borrowed some WD40 and my beater framing hammer, but no luck. I got my 5lb. sledge, but no luck. They tried both of them pushing and pulling, but no luck. D'oh! Fortunately I'd added a cleanout where I tied the DWV line for the addition into the existing line, and they could work from there.
So they started the water running into the laundry sink, and fed the snake in. After about 85' of snake went out (which should have been most of the way to the sewer), the sink started draining. Yay! They kept pushing it in, and I watched from the manhole. We could hear the snake (and all that water running), but still saw nothing even when they got out to the end of the 125' snake. Hmm. They pulled it back, and what should they find? The 25' x 1/4" snake, now nicely wrapped around their 3/4" snake. It appears to have come out completely, though they took some bolt cutters to it to get it off.
It turns out that although the main DWV line angles towards the uphill side when it leaves the house and goes under the addition, it must bend around and tie into the main sewer line below the manhole. Where exactly the laundry drain ties in to it, I don't know. But it's all draining again. Yay!
25' x 1/4" snake? $14. 35' x 3/8" snake? $19. Two plumbers from Roto Rooter for an hour? $321. Being able to flush the toilets again? Priceless.