Let me just say that upgrading my 75gph single DI unit to a 150gph (double 75 membranes) and double DI unit is TOTALLY worth it! The amount of clean water produced compared to waste water is ridiculous! I was filling a small brute can of waste to a 5 gallon jug of clean before and now my clean water is more than the waste! So for those interested in what I did here is the breakdown. I had a unit that had Sediment filter Carbon block Finer carbon block RO 75 gph And a single DI canister I used the RO unit I won in the raffle along with a couple of parts from BRS to do the upgrade. I ordered a DI internal canister (the thing that holds the resin), a bag of resin, a couple valves and a 75 gph RO membrane (both RO have to match). I routed the water in as usual (in my case, through a pump first) into the sediment and carbon blocks and up to the first RO. From here I took the waste water and routed it over to the second RO inlet. Then took both clean lines and T'd them together and ran into the DI unit. I also made sure to have check valves on both clean lines to prevent one line backing up the other since they were being joined. From here it goes through both canisters and out to the clean container. The waste line from the second RO is the waste line. Some may say this isn't necessary but in doing some research, it can help with phosphate and chloramine removal. I don't think our city uses chloramines but I know I have phosphates in the water. Albeit I didn't test for phosphates before I upgraded, but my main concern was reducing waste water. And it has definitely done that as well as pumping out water at least twice as fast if not more! I'm going to have to rethink the idea of putting the waste water in the larger bin with the auto shut off and move it to the clean water bin! This makes me happy! So I also moved the TDS In line to right after the pump because I wanted to see what our home filter was doing and the Out line is after everything. Earlier when I checked the In was 60 and Out was 0 but just now the In was 48 and the Out 0. I'll be moving it back to before the DI stage to keep an eye on the RO membrane output. Took me a minute to plan it all out in my head but I think I got it!