Not quite sure how your setup is but when I do water changes I use a 30g trash can to mix water and a maxijet 1200 to pump the water from the can to the tank. It pumps from the bottom of the can to the top of a 90 which is over 5'. It works just fine.
For auto topoff I put a Y adapter on the outlet for the washer hookup and use a hose to connect to the RO/DI. It then flows into an 18g tub with a lid, it has a float valve to stop the ro/di which has a internal shutoff to stop the flow through the waste valve. From the tub I use an osmoslator auto topoff from Tunze. It has been flawless. Mind you now I have a basement where the hose and RO/DI are and only the small tube from the RO/DI outlet comes into the room where the tank and tub are.
I also use the same maxijet pump to pump the water from the 18g tub into the 30g trash can to fill it with RO/DI water. I fill the 30g half way, then when the 18g fills back up (only a few hours) I fill it the rest of the way. I also use the same maxijet to circulate the water to mix the salt.
When I do the change I siphone 5 5g bucket out of the tank and or sump (I siphon any junk out while siphoning), then pump the water from the 30g into the main tank. Once done I put the pump in the 30g can and stick it back in the closet until next change.
HTH,
Greg