Need help Flushing Coolant

Hi guys, I need a little help flushing my coolant. I've heard of filling the system and running the engine. Than drain and repeat. But that doesn't exactly sound like a good idea to me. I've also heard of draining the system and putting it all back together, then sticking a hose in the radiator cap and let the engine run. I guess you would keep the drain plug open in this procedure. Could somebody explain the latter procedure to me, because I'm not 100% confident that is correct way to do it. Also what is the best way to drain the engine. Thanks

My truck is a 1994, C1500, 5.7L

Surely somebody can help me out here. :disappoin

buy some prestone super flush and follow the directions on the bottle. Fill the system, runn for 10 min. drain. fill with tap water, run for 10, drain, and again. Then change the thermostat while you got the rad empty. Fill with proper mix and you will be good to go.