I do not soak any of my sulcata tortoises, large or small. I do keep water available at all times for them.
They also have a mud hole that they love. The females use it more than the males. The males usually only come to the edge to drink, the females go into the pool for their "beauty treatment," soaking and flipping mud up on their carapaces.
I have never found fecal material in the mud hole, I have no idea if they urinate in it or not. I do find fecal material in their water dishes. It is interesting to watch them drink; they can ingest great amounts of water. My big tortoises will drink for 5 to 10 minutes at a time, but not very often. I have one tortoise that will actually open his mouth in the water; all the others take the water in thru the nares. Sometimes if I startle one that is drinking, it will look up and expel water out of both nares, kind of like soda coming out your nose.
I use the overhead, ratchet-type of sprinklers to water their pasture.This keeps a lot of moisture on their food supply and keeps the ground-level humidity up. They like the rainfall effect of the sprinklers, and will just stand still and let it "rain" on them. I have a small area sprinkler that I use to reach areas the ratchets do not cover. One of the smaller tortoises likes to sit right on top of it.
A puddle from a slowly running hose is also popular with the tortoises.