Fixing a Salt Water Drip from a Clogged Vetus Anti-Siphon Valve (Raw Water Exhaust)

Last summer I noticed salt residue near the autopilot ram and below on the water muffler. It confused me as I couldn’t tell where it came from but I cleaned it up and put it on the watch list. A month into the fall season I realized the source, the air vent for the Vetus Anti-Siphon Valve for the exhaust/sea water.

The purpose of the valve is to keep seawater, from the water muffler, from flowing back into the engine (which could hydrolock the cylinders causing a bunch of damage). With a bit of internet searching I learned that salt can restrict the valve that opens after the engine is shutdown. Normally when the valve opens it allows air to enter the system which drains the raw cooling water out of the hoses. When clogged the air vent will drip salt water. Voila, now to clean it up and put a stop to the messy salt build up in the engine compartment.

Reassembly is simply the reverse order of the steps shown in the pictures.


  • Sandy Marshall July 18, 2021 at 1:43 pm

    Brilliant explanation – thank you

  • Ronan August 5, 2021 at 4:01 am

    Great help to tackling this job, thank you Chris. Valve seemed pretty clean and free moving so will have to wait and see if the water continues to dribble out….

    • Chris French August 6, 2021 at 2:48 pm

      Fingers crossed that it solves your issue.


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