Well, I've this, kinda. I was looking at the plumbing again today. I verified that I still couldn't get the pump to draw any of the remaining water. On the theory that the pump was sucking to hard and causing the alleged "funnel" of water, I partially closed the valve between the tank and the input of the pump. Water started flowing again! AHA! I thought. However no matter how I set the valve, turned the faucet on/off or turned the pump on/off I couldn't recreate the problem. I was able to run the tank dry.
So, I'm not sure what caused the problem but at least have a solution (that worked once at least).
2012 Swift SLX 145RB
2013 Ford F150 XLT Ecoboost Supercrew Short Bed w/ Eaz-Lift Elite WDH