I upgraded my OEM pump within a year of buying my ACE (bought in Fall 2012) and I also added the check valve at that time as cheap insurance. I actually installed by check valve between the pump filter and the pump because I had flex lines that easily incorporated the valve plumbing change; but it probably does not matter if its on the inlet or outlet side of the pump. At least I have not had any backflow FWTank fills since owning the 2013.....but there is always a first time of course.
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