When I used a clog buster pressure jet under the kitchen sink, a bunch of black junk came up into the tub ~20' away. I remember a cleanout on the end of the kitchen line and the bathroom line from the last time I was under the house.
I'm going to find a plumber with a small drain rooter that can be taken down into my crawlspace. And want to inquire about the best cutter head for knocking rusty scale type material from the interior of the pipe.
Do any of these type heads look better than the others for that purpose?