You can salvage as much water as you want up until the point that you disturb the CC bed. Toss the rest at this point. You can have all of your corals and or fish in this water you are intending on salvaging. Just put a powerhead in a big container that can hold it all to keep it circulated. An airstone wont hurt either depending on how long it will take to get this done and rock reaquascaped and tank ready to put inhabitants back in.
Its going to be cloudy for a couple of days whether you rinse it or not. Run a
filter sock over your sump drain and change it every couple of hours to speed up the clearing process. If you dont have any big filter socks.......drive over to my place and ill give you a couple.
Like hop said.....wet sand and a pvc pipe is the way to go.