Dishwashers normally drain through the disposal. There is a place to connect the drain hose. An airgap is intended to prevent water from syphoning back into the DW, but are not really necessary unless required by local code. If you choose not to use an airgap, the drain hose needs to be looped and attached to the underside of the counter so as not to kink. I'm not sure I understand what you me by how much water can come out. The amount of water that comes out of an airgap is the amount that is in the dishwasher.