The only time I bathe my snakes is when they smell bad from slithering in their waste. I just fill a tupperware container with 2 inches of water and put them in. I leave it uncovered. I don't use soap.
My girls just chill there and will sometimes start drinking the water.I usually leave them in for about 10 minutes or until they get restless.
You don't really need to bathe snakes. I just do it to get the crap off them.