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Here is the procedure for cleaning the drains along with diagrams.
Cleaning Water Drain HosesFront water drain hosesFront water drain hoses - 1 - run in A-pillars and end with water drain valve - 2 - in plenum chamber. Can be cleaned from sunroof cut-out - 1 - Front water drain hoses - 2 - Front water drain valve NOTE: For cleaning, it is recommended that you create your own assisting tool out of a speedometer inner cable, approx. 1,500 mm (90.5 in.) long.Rear water drain hosesRear water drain valves - 4 - are installed directly onto sliding/tilting sunroof water drains - 5 - and guided until roof edge under rear lid. Cleaning can be performed from rear end after removing cover - 3 -. - 3 - Cover - 4 - Water drain hose with valve - 5 - Installation unit NOTE: For cleaning, it is recommended to create an assisting tool, e.g. a probe made out of a speedometer inner cable, or similar.