As long as you keep your tank cleaned regularly, you shouldn't worry about any harmful bacteria growing. Snakes are naturally pretty clean animals. I clean my snakes every now and then by cleaning out my sink with tank disinfectant, and then fill it with warm water and let her swim/soak in it. I always put ReptiSafe water conditioner in it before i put her in it though. seems to work well for me!

ps-if anyone sees anything wrong with this, let me know.