I have doubts about a gravity system with canteens though. As the dirty water flows out of the higher canteen, the flow rate will slow drastically due to the partial vacuum created because there is no way for air to enter and replace the escaping water. This is why gravity filter setups are usually done with collapsible containers. You could always drill a hole in the canteen you plan to hold the dirty water with, but I think you would be better served just buying an $8 2 liter Platypus Platy Bottle and filling both 1 quart canteens with the single Platy bottle.

Last edited by JarheadJournalist; 03/24/11 12:37 PM.