The air isn't actually being drawn 'through' the cart but when you are drawing on the eicg the air pressure outside of the cart is reduced and so therefore some of the air in the cart must come out to equalise with the lower pressure being created outside. So in a way it's almost the same thing.
Great post Pete!
You have a gift for stating things in a way that I can easily understand them.
Short, simple and to the point... now why can't I do that?
Thank you...