What Bob & William described is the best arrangement for a normal situation. And I believe it will work for you if you use large lines and eliminate unnecessary hose, bends, etc. Insufficient supply is the problem most of the time when people can't get a DD pump to suck. But if have maximized your supply and are still unable to get the pump to prime with larger lines, etc. then relocating the water supply to between the tank and pump (closer to the pump) and letting it backfill the tank can provide the extra positive pressure necessary to get over the hump and make that happen.
Yes, you are robbing Peter to pay Paul, but in this case Paul is underfed and refuses to work. And technically you're not robbing Peter as he will get the difference between supply and demand, no matter where you place the supply. The only downside to this arrangement is that it does eliminate the ability to put in a float valve, so overflows are possible unless you watch your water level.
