Outdoor Power Equipment and Small Engines - double fuel lines on 2 strokes

Would someone explain to me how the small engine carbs with the primer bulbs with the 2 lines work? Like which line does what?

Generally, one line goes to the carb, and the other goes to the tank and is just open in the tank. The primer bulb pushes fuel and air out the line that is open in the tank, and sucks on the line going to the carb. The other line from the carb to the tank has a fuel filter on the end, in the tank. The suction side of the primer pulls gas through the carb, and the pressure side of the primer pushes it back into the tank, basically filling the carb with fuel so that it can start easily.

Cheese - are you saying that the primer bulb simply moves the fuel through the carb to remove air bubbles and make fresh fuel available at the diaphram? If that's the case, then when the primer bulb is used excessivly you cannot flood the carb?
Thanks,

Generally, yes. Some carbs are designed to actually squirt gas into the carb throat with the primer, but most just fill the carb, and you can push the primer all day without flooding it. Keep in mind that this is just common 2-stroke engines. 4 stroke engines with primers DO flood when pushed too many times.