The first thing I would check is to ensure that the valve on the winterize tube (assuming you don't have a water center?) is fully closed. I missed this one year, and the air leaking in the af tube prevented the pump prime. Also, make sure that the filter cover is on tight and not cracked; another common spot for air to get in.
You can also test the pump draw somewhat by putting the anti-freeze tube into a big bucket of water and setting valves appropriately. Can it draw that water okay?
2011 Jayco X19H (purchased 2015)
2008 Jayco 1007 PUP (purchased new, traded for the X19)
2018 Nissan Titan Midnight Ed.