[bestgenman]

The overflow tank (expansion tank or recovery tank) relies on vacuum to return the fluid to the AH.  I was always fighting leaks in the system from a bad cap or a loose hose from the high water temperature.  Moving the tank to an elevation above the top of the AH stopped all those problems.  It required the use of a tubular tank which 4” pvc fit the application.  You are looking at the sight tube on the end cap.

It has worked flawlessly for a couple of years so far.