I get it from my local reptile shop but they sell it on Amazon around £8 a bag .
It’s easy for when the go a toilet on it just pick it up and put another handful in the vivarium.
i bathe my tortoise twice a day. I prepare some warm water about 90 degrees Fahrenheit and let them soak in the plastic tub for about 20-30 minutes which helps them excrete. Later I give them a quick rinse to clean up and let them eat. By excreting in the plastic tub, the enclosure is cleaner.