Milk jug plastic is a good, opaque material, but I’ve found it becomes brittle and deteriorates over time. My plastic go-to, though not for the same use as you, has been the clear plastic containers that the big-box stores sell things like animal crackers in. I use these for mixing chemicals in, fungicides and the like. And, notably, my Sharpie markings on these don’t last well either.

Lovely tour, as always!