In Ground Pool Empting Problem

[JohnT]

Pool pumps don't have much lift capacity. Eventually the water gets too low for the pum and you need a portable. Make sure your ground water conditions are suited for draining. You could have boat instead of a pool.

[Poconos]

My gut feeling is once you have a solid charge of water to the pump it should be able to suck from the main drain. However, even a tiny air leak, like the fuzz on a tennis ball, will probably let enough air in mess up the suction. When starting without a charge of water self priming pumps won't be able to create enough vacuum to lift more than a couple feet of water at best. You could rent a pump like you suggest or for around $100 buy a sump pump at Home Depot or equivalent if pumping rate isn't much of a concern. For the cost differential you then own the pump.
Al