In the old house I kept them all behind the garage on ex staging fro those little plastic greenhouses and would sort them by size and shape - more or less - and then just blast with a hose.
In this new garden I have a veggie plot - 29m x 25m and we've erected a polytunnel - 8m x 4m - so some serious seed sowing is happening, mostly in coir cells but, as we're effectively starting fresh, I did take all the pots for pricking out and wash them and rinse them properly. A first, but worth the effort for home grown babies.