Yeah it's possible. They usually say just get some tank water in a bucket, toss the fish in, and then sand the tank but I suppose a little at a time you could do.
To wash it do a SMALL amount at a time in a bucket, take a hose and put your thumb over it for pressure, stir up the sand, and tip the bucket a bit to get the nastiness out. It is clean when the water is clear.
A faster way that I did it (kinda and to explain but I'll give it a shot) get high pressure with your thumb and fill the bucket a bit, tip to side slowly and kep going all the way down til it is completely sideways, to keep the sand in you point your high reassure spray toward the side and diagonally a bit inside. What it will do is agitate the sand in a circle and once you find the right spot to point the spray it will stop the sand from coming out by creating a wall of spray and the extra water wil drain over the top of the spray. Like I said it's hard to explain but if you mess around a by and figure out what I mean it'll cut the cleaning time in half. Either way it isn't too had of a project. The biggest problem I ad was putting too much sand in at once when I first started. Makes it take forever