The worst is when they pass a “broody poop” (aka, they saved it up all day/night just for this moment) in a freshly cleaned pool.
One broody poop destroys any attempt to have something nice for the others to swim in. I actually have a smaller pool that I encourage the ducks to go into first as it is easier to dump, and my hope is that they will poop in the small pool and not in the big pool. Sadly, they manage to poop in both, even within minutes. I’m actually procrastinating cleaning the pools right now. After all, why bother?! I will say that I recently got a power washer that I use to clean the pools after emptying them. It’s very satisfying to use.