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Step 3: Locate and Drill: Clevis pin, first picture. I suggest slipping the O ring into the Clevis Pin first. Then insert the Clevis pin into the hole. In this manner, the O ring is sandwiched between the Clevis Pin and the ammo can wall. In my humble opinion, this change will create a more water-tight seal.
This is my version of your project. Instead of shrink tubbing, I used a paper clip. Also, I made it adjustable with 2 pieces of plastic tubbing.See attached pictures.