Adding dry rock to established tank?

you can rinse dry rock and put it directly in if it is from a reliable source.

I would not use a powerwasher - they may pressure heavy metals in/on to the rock. I think the risk is extremely low, but I personally wouldn't use a power washer in this context.

 

I would pressure warsh the dry if I was doing it again.
There is soo much dust in and sand in them, you'll be glad you took the time!

Also, I would get a rubbermaid bid fill it with FRESH made salt water and throw all your rock in there, a power head, heater and let it begin to ghost feed it to get your bacteria going. You can add the bacteria in a bottle solutions when you finally transfer it to the tank and get some fish in there quicker.

Easier to start in a tub than your tank, if it starts to stink, throw in a back of GAC.