Everyone i've ever see clean them, just washes them. Then just spin the water out of them, you can do so with a cordless drill if you make a setup for it or just mount them on your buggy/truggy and rev the engine while on the starter box or off the ground. The holes in the tires will allow the water to escape when they spin. As long as you don't squeeze the wheel when under water it shouldn't soak up very much water.
If i get a chance i'll post a pic of my setup here shortly. It allows the wheel to be taken off and put on a cordless drill to spin the wheels dry.