Muller Vent Exterior - Plastic Vent Muller Exterior Plastic. A teardrop shaped plastic vent. Venturi technique extracts air even while RV is stationary. Features These are a flush fit and cover a recommended opening of 125mm dia . (min 100mm, max 150mm dia). Silicone or caulking should be used to prevent leaks. The narrow end drains the water when travelling and should be pointed to the rear.