If you can find a big enough ceramic dish that's what I use for my pacman frog, one of the plates/bowls that go underneath flower pot. I recommend this if you are worried of it being to cold for him because when I rinse out the dish with hot water the ceramic stays warm. Then if you put abit of room temp water or a little warmer into the dish it doesn't go cold because both the bowl and water are warm. The only problem you may have is finding one deep enough for a big Bullfrog.