I have a Flojet also....use it to pump 75' with a 2' rise using 3/4" hose. Motor gets pretty warm so I take a break between pumping tanks.
I don't think Flojet will pump 300'
Per Flojet Tech Sheet:
Hose Size---------Maximum Hose Length
5/8” (16 mm)---------25 feet (7.5m) max
3/4” (19 mm)---------50 feet (15m) maxRecommended lengths are based on horizontal discharge. Longer discharge runs create higher resistance and may result in the pump motor over heatingFlojet Tech SheetThat garbage disposal set up posted by 'rv2go' most likely would pump 300'