Vetus NLP40 Plastic Waterlock Muffler 40mm 4.5LVetus NLP40 Plastic Waterlock Muffler (40mm 4. 5 Litres) The Vetus NLP40 is a marine exhaust waterlock made from synthetic materials. Due to the design of the waterlock, it also acts as an exhaust sound muffler. Vetus NLP waterlocks feature dual stage functionality, consisting of one lower chamber and one upper chamber. Coolant water and exhaust gas enter the inlet in the bottom chamber, travel up through the central riser tube and then exit through