FWIW, I think you may be living dangerously. I recently had to reconsider what I was doing with my machine and the FloJet supply which has much less potential of disaster than yours. I was putting 3 gallons of water in the supply carboy and only had a one gallon waste container. If there was a failure of a solenoid or whatever I had the potential of pumping 2 gallons onto the floor. With a plumbed in machine but not plumbed out the potential of a massive cleanup is much higher in the event of a failure. And eventually all machines fail.
I now have a 2.5 gallon waste container and limit my supply carboy fill to 2 gallons. No chance of overflow as long as I empty the waste container when I fill the supply.
Suffering from EAS (Espresso Acquisition Syndrome)