I’ve thought about installing a drain tube. They don’t come with it standard.
It would be a good idea I think because if the roller tube ruptures on the downstream side of the roller assembly, it would basically sit there dumping fluid out on top of the tank and down to the ground until you started noticing the concrete getting discolored by the acid.
If you do find a good rubber grommet for the new 2nd hole, please post close-ups and share where you got it!
I just used a flow-vis and it seems like it does the job. I imagine the more check valves you put on the pipes, the more head loss there will be. I figure if the pool pump isn’t running and the acid pump is for some reason, the flow vis will keep enough separation between the acid and heater.
If the power is out, then neither pump should be functioning... so no worries.
It’ll be interesting to see your set-up.