Also, I learned that pea gravel is way too hard to keep clean. But it might work for you? It just sort of collected the poop and then I had rocky poopy yuck.
If you take away food at night, they may not drain a bucket. I mean, really you just need nighttime water if they have nighttime food. I am just paranoid when its 1000000 degrees out otherwise, they don't get nighttime water.
I love your setup. But in answer to your question, I do NOT keep swimming water available at night because it is a HUGE muddy disaster. Only time I keep swimming water is if we're gone for a few days and they have to stay locked up (we have someone keep them fed and watered but they stay...