Can I gravity fill my on board tank?

On my Jayco same setup more or less. I think I can still use the single port to fill the tank via gravity the issue is getting a jug of water that high and holding it there while it empties 10 times +. However I also have the option to use the water pump by changing the valve settings like when winterizing but with different valve settings. On mine it is a bit of pain to get to the valves but is doable I just have to empty out the storage compartment, pull down/ remove the bulkhead panel to get to the valves. They have a little cutout but they are mistaken if they think you can see much less reach the valves from where the cutout is maybe if it were 5 time the size of the 6 square inch removable cutout. I plan on making a new removable cutout in the proper place and size to aid in that as well as winterizing. Another option might be to use a drill mounted pump I have one I have used to empty fuel tanks with a cordless drill it has suction on one end and discharge on the other. IT will pull 10 gallons of fuel out in a few minutes (obviously if I were to do this I would strictly use a new pump for water only). The pump is pretty cheap such as this one http://www.acehardware.com/product/index.jsp?productId=1278825&KPID=960087&pla=pla_960087