About once a year I have to snake my kitchen drain line using a motorized snake like the RotoRooter folks use. I finally bought a camera to inspect the drain and found this about 10-15' past the sink drain:
This is a 1.5" PVC drain. It looks like something is peeling from the pipe wall. We're on a septic tank, so we're very careful about what goes down the drain - most organic matter goes into the compost bucket. In addition, we're vegetarians, so no animal fat is run down the drain. Nothing other than the kitchen sink feeds into this section of drain. About once a month we pour a couple of gallons of boiling water down the drain (in addition to boiling water drained from pasta and such). Over the years I've tried various chemical drain cleaners to no effect.
What might this be and more importantly, how do I clear it out?