nasty rock

[Realshow]

I have about 300 lbs of rock that was live a month & a half ago. The person I bought the tank from also had the rock. It was covered with palys shrooms & algae. It was all removed straight from the tank & stuck outside dirty to dry.
My question is, how is the best way to clean this stuff up? I have thought of using a prtessure washer & blasting off a bunch of the nasty chunks of junk & then proceed to slowly cure it as recomended by Myka's thread. In the stage this rock is on now do I still need to use saltwater for it or would it be ok to just use freshwater & give constant flushes until it gets to a stage not as foul as it is now.
Cheers!