My dad was in the Automotive Radiator industry for 40 years . So i have alot of education on cooling systems .
I never heard of a pump being hooked up to flush a system . Is this a owners manual or a book such as Chiltons or Haynes suggesting a flush ? Unless your system is over heating or grossly dirty there is no reason to flush a system its just a service shops sell you to get a $ 100 out of you plus coolant . If your radiator is dirty the only thing that will clean it and un clog it is to be rodded out out ,or replaced . Antifreeze does not physically ware out it gets dirty and the corrosion properties break down only if you do not care for your coolant , if you keep a good 50/50 miuxture and add a good anti rust corrosion additive to your cooling system . The anti corrosion additives are made from water soluble oil you can buy this buy the gallon at Napa i use this religiously and have cooling systems with coolant that is 10 to 20 years old with no issues , i add about 1 cup a year ,you can uyse the additives that is on the market , i just prefer my method .