So they can get wet? I realized they would be in the water soon, but wasn't sure how quickly. I will need to look for brewers yeast.
You want the hole to be big enough for their heads to fit, but not their whole bodies... yes, they can get wet right away, just have to watch for waterlogging and sinking when bathing and keep them warm... be careful of them catching a chill... toweling them off and a hair dryer on low helps tons...
Brewers yeast or can be called nutritional yeast... Amazon might be your best bet if you can't find it close to you... but a lot of vitamin stores carry it...
Oh, and put their water containers in pie tins or shallow baking dishes filled with clean rocks/marbles/glass blobs... they will be very messy, but that will catch a lot of the water and keep them from spreading it around as much...