I always leave sand baths in my hamsters cage so they can use it whenever they want to.
I use the Tiny Friends Farm Bathing Sand (
http://www.petsathome.com/shop/en/pe...-sand-15-litre)
Depending upon what species of hamster you have it will determine the way they use the sand bath - dwarfs and Chinese tend to roll around in the sand so use it as a sand bath whereas Syrians use their sand bath as their toilet - this makes spot cleaning easier and keep the cage cleaner (also they don’t seem to roll around like dwarfs would do)