This is my water prep station. The top is the RO reservoir, the bottom is saltwater. The RO/DI system runs to a tee that feeds float valves in both trash cans. There is a ball valve I can cut off on the line to the saltwater trash can so that once I get the salinity right I can use it little by little without it being topped off with RO/DI again until I want it to be. The pump in the bottom of the saltwater trash can feeds up to the black hose connected to the PVC that goes around the front right leg. That is where I have a tee and ball valve to fill a bucket or water container. The valve going back to the trash can allows me to cut off that flow and have all the water flow from the pump go to the bucket or container. The pipe going back in to the trash can goes all the way to the bottom to mix any salt that may settle when I add it. The saltwater trash can lid has a door cut in the middle of it and is on hinges so that I can easily add salt and get a water sample to test the salinity. The hinges are coated in silicone to reduce rusting. The water supply and waste lines run to the ceiling and then over about 6 feet to the water connections shared with the washing machine. The end result is easy water prep with no hoses to drip as I move them around.
The water supply to the RO/DI has a valve that I keep off all the time except when I actually need to fill the trash cans. This prevents a leak having an endless supply of water.
A lot of other designs have external recirculation pumps for mixing the saltwater, but I want as few things hard plumbed through the trash cans as possible. There is nothing going through the side except the float valves (which you have to) and the drain from the RO (I couldn’t figure out a better way to do it). I also don’t think I need the power that external pumps can supply.