Hi mikel988,
You have indeed experienced a bit of overwatering. The hotter your roots get the less oxygen they get, this leads to root rot which is really what 'overwatering' is, or becomes if not dealt with immediately. If your summers get hot forget about growing above the ground, instead bury your container in the ground so it stays cool from the surrounding soil. If that's not an option then use the biggest pot you can and keep the pot shaded at all times, and you might make it through. Also make sure your soil mix is very airy, a heavy wet soil is certain death in hot weather. And don't place the pot on a hard heat conductive surface, better to stand it on some soil. But again, you really should bury your pot in the ground. Oh, and your buckets do have draining holes on the bottom and the water can escape, right? If not, get it done ASAP.

I hope you beat the heat!