My suggestion was going to be to have one barrel for RODI and another to mix SW. Have a pump in the SW with enough power (volume & pressure) to get to your tank/sump. You can use the same pump to remove water from your tank/sump to fill by just moving it back into the barrel. I can do 10-20 gal WC from my barrel that is 60+ feet away in about 10 minutes. Just a thought. Not exactly automated, but when I perform a WC, I prefer to actively siphon the sandbed or blow off the rocks and vacuum out that water. It leaves some corals exposed for about 10-15 minutes. Then I quickly fill it back up with a flip of a switch.
Also, for your smaller tanks. What I am currently doing is using a small pump inside a 5 gallon bucket with a foot switch to fill up my smaller tanks upstairs. No more trying to lift the bucket to fill tanks or using smaller transfer containers either. I have one bucket for the dirty water and the other already filled and ready. I am able to perform a 4-5 gal WC in about 10-15 minutes.
Mind sharing pictures of your set up/ links to what pumps your using.
Thats also part of the reason I kept the 2nd barrel, I planed to use one to mix saltwater. One is already used to hold rodi water. The longest run I would have is currently like 35 feet if a pump was at the bottom of the rodi barrel in my kitchen, to reach the top of the other barrel that would be in my garage where the salt could be mixed and despensed to the sump on the tank.
I guess after hearing you guys describe your setups. What I could envision for my system.
1.) Is a pump Permanently left at the bottom of the rodi container with a hose I can roll up neatly somehow capable of reaching the salt mixing barrel in the garage (maybe a switch or a smart outlet where I could instantly turn the pump off while in the garage ensuring it doesn't over fill it, or some type of automation shut of sensor like atos have).
2.) The saltwater mixing container would have a heater and some pump or wave maker capable left Permanently in it to mix and heat the water. It could also have a twin pump like the one in the rodi container with a hose that can also be rolled up when not needed that can reach the frag tank and the 200gallon tank.
3.)As far as draining the water from the 200gallon tank maybe a 3rd identical pump could also be used with a hose capable of reaching a sink. Or possibly a spot on the manifold with a quick connect for a hose to be used to drain water.
I do understand that one pump can probably be used to do all three but seems less trouble to not have to transport pumps around the house trying not to drip water everywhere. Storage Space isn’t really a issue though I doubt I would want both barrels in my kitchen even though it's always a option down the road. If I can find something nicer than a barrel that stacks and isn’t a eyesore.
***The Idea I would like the best in a perfect world would be a quick connect If there is a method that would work to where I could leave the pumps in each barrel and length or hose or pipe to reach just outside the barrel with a permanent quick connector of some type. That way I would only really need one hose that could be used to connect to the outside of each barrel to just move the water than just put that single hose away when not needed.***