You might expect water to flow faster from a full bottle than a nearly empty one — a Mariotte siphon proves that wrong. In this project, you drill a hole in the cap of a 2-liter bottle, thread a vent tube through so it reaches partway down, and cut an outlet hole near the base. Fill it, seal the cap, and measure how much water comes out in a set amount of time. The vent tube controls the pressure at the outlet, so the flow stays constant whether the bottle is full or nearly empty — the same principle farmers use to apply fertilizer evenly across a field.