The ones I have are a mixture of Anchor brand and Pyrex. I've found them at Dollar General and Walmart. Some of them came in packs (like 3 or 4-all the same size). They hold 2 cups. There's also some 4 cups ones, but I don't use them as often, as none of my snakes are really partial to soaking. I like them well enough. It's great to just pull water bowls out one day during the week, run them all through the dishwasher, and presto! clean bowls. One of my big females (actually-the one pairing with the mojave), likes to perch on top of hers and tip it over. She hasn't done it since I moved her to a 41qt tub though...
I don't think that's so much the case as the boys are smallish.Both girls are around the 2kg mark and the boys are both around the 1kg mark.