So I got home after a long morning riding my bike up and down the hills of Santa Cruz, pull off my salt-stained gear, hop in the shower, and wouldn't you know it but the drain is plugged.
Thankfully my Trump-disapproved low-flow shower head wasn't filling the shower pan too quickly so I had plenty of time to soap up and rinse clean, but that wasn't exactly going to be a viable long term solution.
Now the drain had been somewhat slow flowing for a while now. Usually when I'd start a shower, the drain would back up for a moment, threaten to overflow the drain grate, but then catch up with itself and not cause any fuss for the remainder of my bathing. I had previously attempted to snake the drain, but the snake had always come out perfectly clean, leaving me rather puzzled to say the least.
But, as the situation had clearly deteriorated, I brought out the snake again to give it a second shot.
At first the results seemed to mirror previous attempts. I never seemed to hit a blockage, never got anything wrapped up in the snake, never got the water to flow. My plumbing line does have a cleanout outside, so I tried running the snake down there and as I expected, given that no other drain on that line had any issues, I didn't find a blockage there either.
I felt a little defeated and took a break to eat lunch, pondering just calling a plumber to go shimmy into the crawlspace and rip out and redo the pipe for the shower, but I went back and gave it another shot once I'd gotten some food in my belly.
I poured a few kettles full of boiling water down the drain and ran the snake again, and finally this time it latched onto something. It took quite a bit of force to yank it out, but when it came loose it pulled up a rather disgusting looking wad of matted hair, fabric fibers, and bits of carpet? Lord only knows what the previous owners were washing in that shower.
Still, the water wasn't draining, so I went at it again. It seemed to be pretty hit or miss whether I'd latch onto something or not, but after a few more lucky hooks I seemed to get the bulk of the clog cleared out.
When I poked my head into the crawlspace to have a look at the pipes the problem became quite apparent. The shower pan itself was plumbed with nice, smooth ABS pipe, but just past the trap it transitioned to galvanized steel pipe, which threaded into a cast iron tee fitting at the far end that served as the vent going up and the drain going down. Judging by the length of snake I had to feed in, and the fact that I was clearly hitting the far wall of the tee fitting before latching onto the clog, it was apparent that the threaded end of the pipe had been rusting internally and this flaky rust had been what was catching all the fibers as the water flowed over the corner of the tee, forming a clog just below it in the vertical pipe.
At some point I might have to go down there and replace the galvanized pipe with a length of ABS, but for now the drain is working so I'm just going to leave well enough alone, and be glad that I'm back up to 2 working showers again.