[banditpowdercoat]

OK, with that first link, having an electric pump on there, Now I can see how it will work.

When the RO water is used, the pressure in the pressure sw drops, causeing the elec pump to turn on. Because the waste and inlet water are taken from the house supplys, they are both at same pressure.
The pump then increases the membrane inlet pressure higher than the waste presure. Waste is forced back through the hot water line.

BUT, because the Hot Water is acctually plumbed from the same source as the cold, the waste acctually flows backwards through the Hot water line, back towards the Hot Water Tank, and eventually out the tank's inlet, to the cold line.

I can see this system is best for a small RO system. If your like me, and make 30g+ of RO at once. Well, at a 4:1 ratio, thats 120g of waste, best case, you and I know it's more like 200g waste. Most HW tanks are what 40g? So, you would in essence be draining your hot water tank 5 times, and recirculating through your RO system.

Now, making a gallon of water here, cup there, I can see that being a great solution