It is fun, isn't it? When my muscovies were little, DD and I used to let them have a bath everyday. Muscovies are a little different than the mallard based ducks in that they don't like to swim as much, and don't really want to be out of their depth. Yet they have the same need to have water deep enough to clear the nostrils. We used to run the bath with enough water they could sit on the surface but still touch the bottom. They would dive under and splash water up over themselves and just have a blast. They always "emptied out" in the tub too - it was a mess at the end of every play session.
After they got moved outside, I put a kiddie wading pool out for them and keep 4-6" of water in it for them - they still get in it every day.
I clean out my tub about 10+ times a day - seriously! They make quite the mess... I have a large baking pan (ha.. how inappropriate is that for ducks to splash in? lol) and then a little plastic drawer on the other end of the tub with papers and a food dish for them. They have the whole middle of the tub to walk around... I have all the materials needed to get their duck house put down at the lagoon with hardware cloth, posts, chicken wire, pool... I'm going to work on it this weekend and hope to put them down there during the day in a few more weeks (still bring them in at night because of predators/temperatures) and then hopefully keep them down there in about another 4 weeks. I have some nice materials to make a wind-break for them on the north and east side of the lagoon too where their dog house will be sitting against the lagoon fence.