I find it next to impossible to get the grunge out of fixer bottles. That is why I use old milk jugs for fixer and when they get dirty with this stuff, I just toss them! It is not worth the effort to make good negatives and have them messed up with spots from this junk falling off the edge of the jug and getting into the emulsion and turning up as white specks on the print.

Loose the jug!