Understanding the cooling system

I have a 98 grand am with the 6 cyl and just replaced the water pump. With this system there is only the cap on the reserve tank. ALthough its all right there i am still having trouble visualizing whats going on. The Hot water exits forward from the pump goes to the y where one tube runs up to the reserve tank. From here on the pass side the coolant goes into the radiator.

After i have bleed all the air from the system i set the coolant level to the line on the reserve tank. Is it gravity that sets this level because it looks like the line is at about the top of the water pump? How does the coolant not go up the reserve tube if the water pump is presurizing that line when the engine is running.

Thanks.

Because its on the suction side. The water pump sucks coolant from the lower hose and pushes it through the engine and out the lower hose. I think you are thinking that the water pump is pushing coolant through the lower hose.