Sure, you can rinse out your sand with pure RO water... and your live rock can be washed in some saltwater that you mixed up with RO + Salt. You could take a brand new never used toothbrush or bristle brush and get some of the junk off the rock. I wouldn't put your live rock in straight RO water though because there will will be some things living on it.
Once you wash everything off, get your tank set back up and add a "polyfilter pad" to the filtration system - the filter pad changes colors as to what happened in the tank. if it changes blue, then it was the copper... the filter will remove as much copper in the water column as it can. Another good idea is to add some macroalgaes to your new setup - harvesting the macroalgae out of the tank will remove some of the heavy metals as well.
Being that it was only a gallon of uncured tap water, it was most likely chlorine / chloramines that caused the tank crash and not copper. But, it might be that it was copper.
Sorry for your losses and I hope you stay in the hobby.
By the way, welcome to the forums, I hope you enjoy your stay.
