Some budgies do not even like to bathe, I have one of these.
Budget loves a bath, he will use anything that is wet to roll around on, or he loves to go under the kitchen tap whilst I hold him in my cupped hands. Fifo will bathe in a bowl that I place some greens in the bottom of and then add a small amount of water from the tap. I usually simply put enough so they can spread their wings and sit and roll around. My guys wouldn't go near the bath they drink from theirs. Blue gets a misting with tap water every now and then especially if moulting. As he isn't brave enough to have a go .