Air vents for under the waterline exhaust systems. With adjustable and detachable valve/pipe-to-hose for easy maintenance.If the point where the cooling water is injected into the exhaust is less than 15cm above the waterline, when the engine is stopped, the cooling water can enter the exhaust system and then into the engine. Such risk may be prevented by installing an anti-siphon at least 40 cm above the waterline.