I have several pots that started out as bowls, from when my son was a potter. For the one or two that don't readily let the water drain through, my simple answer is to put the pot on top of a couple of chopsticks--that elevates them enough for drainage and air circulation.
You might consider starting a thread one of these days to show some other pots from your collection as well. Sounds like you were in the right place at the right time to land a treasure trove.