I was completely out of DPD power, the CC reagent, and CYA reagent. Everything else was 2.5 seasons old and had been left out in the heat/sun a couple times, plus some of the bottles were crusting over and were hard to get drops out of. I’m sure they could be cleaned but I thought for the relative cost of a refill kit vs clearing up a swamp I’d just start fresh.
Also ordered a SampleSizer and enough extra cylinders and Stir Bars to be able to do all my testing without ever “doing the dishes”
To answer OP's question, I think it's a good idea to pour them all into a large bucket and then dilute them down with water and pour them out in the woods or simply down the drain. The concentrations are very low anyway and diluting them in a bucket renders them virtually inert.
I see no point in squeezing every last nickel out of expired reagents.
Taylor says to use them for no longer than a year when stored correctly. That being said I had an aquarium setup with reagents that were 5 years old and had no issues with bad tests for water quality. I tested it against a new test kit and the local pet store, both read the same.
To dispose of them put them in a gallon of water and put down the sink. Many are naturally occuring anyway and generally septic safe. Always pour the reagent into the water, not the water into the reagent.
I would just like to add it is relatively easy to pop the tops off the liquid bottles. First few years I was either squeezing them as hard as possible trying to get them empty or cutting them with a razor Finally one popped off as I was messing with it and I was like "Oh".