I think predatory fins has a set up that does what your talking about (at least on some of their tanks/rack system), not sure if they would respond but could shoot them an email. Could also look into external overflows/pvc overflows. . .
I’m looking into doing the same thing. . . Eventually. . .
I have 19 tanks, 250 gallons of water. I use a Tetra submersible pond pump for draining (got it at the pond section at the home store), and run a tube from the pump to the floor drain in the next room. You could run it into a sink as well, but it will have a lower flow rate if the water has to climb. I also have a water grade hose running from the tap for filling.
Once I have the drain pump and hose all set up, I drop the drain pump into the first tank until the desired amount has been drained, then move the drain pump to the second tank. Using a Python hook
I fill the first tank while the second tank is draining. I have a small container with Prime and an eyedropper for dispensing. A standard eyedropper is 1 mil, one eyedropper for each 10G's. Then I just move from tank to tank.
It cut my water change time in half. With the pump and the fill hose going at the same time, I can move 250 gallons of water in about 45 minutes (125 out, 125 in). That include setting up the drain tube and fill hose.
I'll look and see what the gallons per hour is on the pump. I do remember getting a smaller one first, but it wouldn't keep up with the fill hose, so the fill hose was idle part of the time. Once I got a bigger pump, they're close in volume, so by the time this one is filled, the next one is drained.
I use a hose attachment between the hose and the Python hook that lets me turn the water flow on and off so I can move the hook from one tank to the other.
Before I start the fill hose in a tank, I use the eyedropper to dose conditioner. I then set the eyedropper on the aquarium cover so I'll know it's been conditioned before I start filling. It becomes a repetitive dance, so if I don't do that, I second guess whether I put in conditioner. In the years I've been using this system, there was once when I came back later and the whole tank was dead. I assume I missed dosing that one.
I'm still amazed at how quickly I can move that volume of water.
Do not, do not, do not let yourself get distracted when that fill hose is turned on. I know from messy experiences. The phone rings, the radio or TV has something interesting, then you hear the sound of water gushing onto the floor.
When moving the pump, grab the plastic hose rather than the cord. It's not only easier on the cord, you will have much more control over the pump. If you grab it by the cord, it can swing back and forth and possibly crack the glass.
I'd guess the entire cost was around $100. I think the vinyl tubing was more than the pump.
I think I might have some photos. I'll look and post them if I find them.