Hi Sew, GMTA! I submerge pots too. I'm usually doing it to evict ant colonies, and make sure there's no spiders in the pots, or any creepy-crawlies that need to breathe. They will come out or drown.
Dish soap has chemicals in it that can be unpleasant for some plants, and not necessary for pesticide purposes. There is horticultural pesticidal soap, which is intended for use on plants (and OK to discard on the ground if in a tub of water.) Dissolving mosquito dunks in the tub would be an alternative also.
