I use a python to sift the sand and dump the water into a 50gal garbage can... then empty the water out side...I should mention i have (2) 50gal garbage cans one empty and one full of RO
...I then have a dedicated RIO pump with a 3/4" hose connected, I mix my salt in the garbage by running the RIO inside the garbage can turbulating the water... I do that for about 15-20mins so the salt is completely dissolved. I then use the RIO to pump the water back into the tank...
PS. I have the inside of the can marked to 35gals, just so i know how much water i'm removing and still allows the can to be moved with water in it.
I started doing it this way 10yrs ago when i upgraded from my 55g to my 125g... I wanted to work smarter not harder, (pouring buckets, whatta mess). A side aspect was the salt wasn't going into the tank poorly dissolved and there was no splashing as the pump put the water into the tank very smoothly and the water was at room temperature.. I didn't add the RO
until a few yrs ago...