It all depends on the tan and how old it is. If you don't know the history for sure, use luke warm water and add 1/4 pound of salt per gallon, along with a relaxing agent from one of the tanning suppliers. Just follow the directions for amount of it. The big reason for the relaxing agent is in case the tannery kicked the skin, which puts a heavy, almost impenetrable grease in the leather, water will just about bead up on the skin and never soak it up, the relaxing agent helps cut some of the kicking grease so water can soak in. Submerge the skin for maybe 20 minutes, do some pulling on it and you'll see if it's wetting up. When it looks like it's at least getting moisture to the pint there's no more dry spots, rinse it in clear water to get the salt out, drain well and bag overnight.
If it's a fresh skin that hasn't been kicked, especially something light like a fox or coyote, just soak the head and paws in plain water for a few minutes, and sponge down the leather, this way it will soak without wetting all the fur back up.