Water Pump loses prime when water tank level is 1/3 full

RKW, what I want to know is this -- how did you get your pump to empty your tank completely so that only a little dribbled out?? Is the outflow tube mounted on the lowest point of the tank? If so, congratulations!

Ours was not, so we had it re-installed at the low point. And I put in supports, like SoundGuy did, to combat the dreaded "saggy belly" phenomenon. (Too bad it only works on RVs and not on humans.) . ;)