In the 5 years that I had my 180 gallon set up, I had my RO/DI plumbed directly into my sump with a float valve and I also had it "t'd" to go to a rubbermaid brute trash can with a float valve for fresh water for making salt water...I used the john guest Ts that also had a shut off lever on them. whenever I did a water change I simply shut off the valve that went to the sump so fresh water would not go flowing into the sump while I was doing the water change... then just turned it back in the on position when finished. VERY SIMPLE and NOT ONE TIME did I have any mishaps with this set up. Going to do this again with my new 120. No pumps, no electricity, no problems.