At home, I dump the fixer, usually 1-2 liter bottles, down the drain. My volumne as of recently had decreased a lot at home since I havent had much time at all.
At work, the fixer is collected in large marked containers that are taken out once they fill up by whatever hazmat/recovery people maintenance calls up.
At home, I mark off the number of rolls I fix per liter (max of 24, 36exp rolls in rapid fix) and test paper fixer with hypo check. At work I only use hypo check on fixer to text exhaustion.