#19 Do NOT (and I repeat, DO NOT) intend to pour the used developer (or whatever) directly in the tank that will be used to drop at at the recycling facility <That is, unless you are 150% SURE that there is enough room in said tank>... Guess how I decided on this one ? ;-)
Yesterday was a developing session, and a rather awkward one... Spilled stop bath while opening the bottle, spilled developer when I decided about #19 above, fixed the film and, only to be sure, decided to run a clip test only to discover the fix was exhausted... So fix again, and I have to plan on refixing the films from last week, just in case...
So #20 Regularly run a clip-test of fixer, even if you keep track of the number of films you developed (I was in the ballpark for this fixer batch...)