We have 8 ducks. I made a pond for them really simply, its about 3ft x 6ft and only about 1ft deep. I built it over a couple of soak away boxes a d put a plug in the bottom so emptying it just means pulling the plug, and I have 2 big water butts that collect rain water from the house to fill it. Takes about 130gallons. I also got a pump and filter kit, pontec 10000. Works really well, water only stays really clear for a couple of days but it's not bad, and certainly doesn't smell even with 8 of them in there all day and night. There is very little left in the bottom when I do empty it. I empty it once a week and have to clean the filter housing out, but doesn't take very long, to empty the pond, refill it and clean the filter. Ducks all in good health. 1 thing I have not tried yet is just cleaning the filter out and topping up the water, the ducks probably kick 1/4 of the water out in a week between drinking and messing about, and seeing what happens. May try that and post results. It may be that I could get away with emptying it once every 2 or 3 weeks, but as its winter here and the water buts are filling in a week its not really an issue.