I am very sad (!) - I keep them in my potting shed. I wash them all after use, but I have so many that I usually have a washing day on the lawn in summer. They are stored stacked in large (14inch) black bins, grouped by size. The bins stand on a shelf made from plastic window sill turned up so there is a rim to stop them falling off and I have the size in cm marked beneath each bin on the shelf edge.
That's the theory.
In practice there are a lot of pots which need to be washed stacked on the floor. And seed trays and those six pack modules, all of which I used earlier this year to grow veg.......
In short, I have plenty of clean ones but the dirty ones are taking over the asylum
Oh, and all my special orchid pots are kept in the house - they don't mix with the common pots!!
Regards
Heather