The trick to successfully blowing our water line to winterize your trailer is low air pressure but lots of volume. The tire chuck adapters are not only a PITA to use but they are very restrictive, often not providing the air volume required to properly blow the water from the lines.
I have documented my solution pictured below which is both convenient to use, not restrictive and easy to build. I have been using this adapter on 3 trailer for the past 2 years and it works great.
Details of building it are on my blog.
Click Here For the Blog
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