Ive been using Clorxa Clean up. It smells like bleach. I know not to use Windex cause of the amonina smell....ha, ha, catching on
Water, bleach, and dish soap. We've always used that combo, and they use it at the animal shelter I volunteer at, as well.
I use Simple Green and let it dry for a few hours in direct sunlight too. We have 2 boxes so it's no problem to be without one for a few.
Are you rinsing it well after cleaning? I've read that the plastic litter boxes, over a period of time and from cat scratches, break down and will start holding odors. May be time to just replace it.
We have 11 cats, don't use ordinary litter boxes instead we use xtra large tubs we get at Tractor and supply. 2 are kept in the basement where 10 cats sleep. Down there we use fine wood shavings along with cedar shavings on the bottoms. Upstairs we use litter/have a diabetic cat that requires injections 2x's daily. When we power wash the boxes I soak them with vinegar and some water for an hour or so, rinse then fine spray with water and vinegar. The tubs we get are really great, wouldn't go back to litter boxes at all. Now if we could afford 4-5 of the automatics, that would be different.
Plastic does get pitted, but you can keep it out of the landfill for a while by sealing it with a floor sealer or with paste wax.
About the plastic absorbing stink over time: I had one that I retired for that very reason. I used it in the utility yard for potting soil and various yard activities like that. After about a year of exposure to the elements/soil/etc, the smell seemed to have lifted from the plastic and it could be used as a litter box again if needed.
I just empty the litter, and use a scrub brush, water and a squirt of dish soap.
I have never noticed any odor and just replaced a five year old box.