Cooling system air vent valve.

Going to drain and flush 2000 Venture cooling system and like to know where the two brass screws for air vent valves are located. Curious because in another thread here someone said the heater core is high so when you drain the system the heater core must be purged of air. How do I do that? I know an air bubble in a cooling system is not good because if it's in the engine it creates a super-hot hot spot and it can crack a cylinder head.

EDIT: I found them one on each side of the hose that runs in front of the valve cover. Don't run the engine with the screws out. Fill up as best you can then remove screws and with radiator cap on fill the screw holes to overflowing then replace screws, Be gentle, brass threads strip easy.

Decided when I get it flushed good I'm going with the universal anti-freeze that works with Prestone green stuff or pink Dex Cool. Friend of mine works in a radiator and AC repair shop and said they see lots of Dex-cool cooling systems with jelly looking stuff in them. EDIT: I flushed it ten times meaning I drained the cooling system then filled with plain water and drive it for fifteen minutes then drained again and refilled then finally filed with 50% universal antifreeze and I'm done with DexCool-DeathCool. For kicks, I put in three tablespoons of soda thinking it will neutralize any acidity.