I have 1 (what I'm pretty sure is a white campbell) duck, and 4 chickens. When she was 2-3 weeks I used a plastic cat litter box that our cat never used. At 4-5 weeks she is using a large plastic round tub that we used to put muddy shoes in, but I am looking into a kiddie pool soon so she can rocket around more like she loves. Two questions: how deep does it need to be? Deep enough that there is an area where she can't touch? Also has anyone had problems with their chickens getting into the pool? All the chickens love their duck companion and when I first put the tub outside and let her swim in it the little RIR thought she would see what being a duck really feels like and jump in too. I scooped her right back out again and she fluttered her feathers and turned her beak up and none of them have tried it since, so I'm thinking that they "get" that it's a duck thing and not really for them, just like the duck eventually decided that perching wasn't for her when I put a large stick in the brooder when they were 3 weeks.
I searched all over my yard for something that would work that was just right. I found in the shed about 10 of the kids 3 foot long sleds. Worked perfect, for the younger ducks I put stones on the inside edge so they can climb out and a ramp on the outside. The bigger pekings use there sled to swim in, and prefer it to the sandbox turtle i filled with water for them. It fits all 5 of the big ones and a separate one for the other 8 younger ones at three weeks old.