I usually only give my corn a bath when he's having trouble shedding. He's rather hydrophobic so I try not to torture him unnecessarily
. I also give him baths when he smells a bit and it makes him smell all nice and clean.
Some corns love taking baths and even soak voluntarily in large water bowls but others (like mine) have to be forced into taking a bath.
Since mine is still rather small (15 inches) I usually plug up the bathroom sink and fill it with tepid water and then :
lunk:: drop him in. (well not literally but i put him in) He struggles around for 5 mins or so (15-20 mins if it's for shedding purposes) and then I take him out and dry him off with his own special fluffy towel.