My Darwin, a 3 month old redfoot, poops every day while he soaks, sometimes a few times ... after more than month living with him, I've only found one poop in his enclosure.
As often as it needs to. Poop and pee can be hard to find in the enclosure when a tortoise is very small.
In a well-hydrated tortoise, urate can be very small and infrequent.
Soak daily in warm water water for at least 20 minutes in a large, flat-bottomed bowl that your tort can march about in and your tort is more likely to perform in the soak water
A washing up bowl is great for soaks because your tort can’t see over or through it and the larger volume of water cools more slowly