Look at it this way. It only takes a small amount of water like a teaspoons at a time lying along a seam to do the damage Syd describes and that a lot of us have been seeing for more than 25 years in my case in all makes and models of aircraft. We had a bad example in a rubber bag type Cessna-182 that had snap loose in each tank. After the crash about a mile from the airport over a quart of water was found in each tank. The owner had drained the usual clear vial of fuel as he had been taught and thought he was ok. We now have several Cessna AD's as a result. some for fuel caps seals and some for trapped water. They tell us to do a
check by pushing the tail clear to the ground and seeing if water is found in any amount as one of the checks to be done. It only takes a small amount to ruin your day and corrode your tanks. My header tank had severe corrosion around the outlet area from a few standing drops something less than a teaspoon. I use the solvent sprayer wand to vacuum out the water and pick up the dust particles that are there with it./tom
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