I have a 5 gallon waterer but my ducks drink up the water so fast! So mainly I just use a kidde pool.
I have been trying to find a bigger waterer for them.
Here is their setup.
I use a 3 gallon rubber bowl. All of my duck are adults and they havn't tip it over! I hated it when my ducks were that age. They got everything dirty and wet!
Good luck!