What I have found out is "usually" when the pump will not prime, it is because there is air in the system somewhere. (Like did you drain the water heater, and forget to bypass it)? Or maybe did you forget to close the tube that siphons from the fresh water tank? Just sayin, I have not had any problems yet, in taking the filter out of the holder, then allowing the pink to fill up the holder.
I started with nothing, and still have most of it left
2001 Jayco KIWI 23B
2003 Jeep Grand Cherokee 4.7 AWD