You might take another look at the way I plumb them...from
Your Previous Thread
1/2" poly braid hose from the rinse water tank with a wide open ball valve for servicing.
1/4" LLDPE tubing from the
soap and wax tanks to a "Y" fitting (PISCO, SMC, John Guest) on the other inlet port.
Now, I must add...my rinse tanks are at the same level as the pump mounting rails while the
soap & wax tanks are elevated 3'-4' above the pump stand. I've never had issues with
soap/wax suction and never have to throttle the water supply valves.
If your
soap/wax tanks have additional capacity you might just try raising the Hydrominder floats and fill them up. Lowering the rinse water level might help, too...as long as you don't starve the pumps.
But, there's nothing wrong with throttling...or using MEP's check valve. Just don't cavitate the pumps. Close the ball valve until the pump starts "rattling" and then crack the valve open until the rattling stops. I've done it many times rather than replumbing the entire system.