In Ground Pool Empting Problem

I live in Katy/Houston Texas and have an in ground salt water 42 ft cement and white plaster type pool.

The store I use says my hardness at 570 ppm is too high and that best solution is to drain 3-4 ft and refill. When doing that I'd like to fully drain and clean some marks built up on the bottom plus I have a few crumbs of sandstone from coping that have "glued" themselves onto the plaster.

My primary problem is empyting the pool. I've put the "octopus" valve on my DE filter to flush and initially all went well with water steadily being pumped out of pool. Then as water level dropped the 2 skimmers started to starve and I placed two tennis balls in them to force a vacuum to the bottom of pool's two returns. But the pump still cycles between gas locking and water. Possibly the bottom returns are partially plugged and the pump overwhelms inflow thus cycling? So next I removed one of tennis balls and placed hose in skimmer hole and into pool after first vacating hose of air to pull water from there. Same problem. Lastly I unscrewed the chlorine generator and put a tennis ball in the hole thinking that maybe I was getting air backwards in the system from the nozzle water returns. Same problem.

Advice appreciated . . . go rent a water pump for the day?

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.

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