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How To Adjust The O Rings For A Perfect Fit

Wrap about 30 feet of dental floss tightly and evenly into the gap between the end of the plug and the end of the pipe on the piston. Leave a loose “tail” of a few inches.

Place the o-rings over the dental floss, and check the fit of your nearly completed seal into the open end of the barrel. It should just barely fit with a little pressure. If it is too tight, simply pull a few inches of the dental floss at a time out from beneath the o-rings, and test until you get the right fit in the barrel. You don't even need to remove the o-rings unless you need to add more floss. When the seal is working properly, trim off the loose floss and you're done.

There is a little bit of trial and error required here, but after the 2nd or 3rd water gun for me I had a pretty good feel for what amount of pressure the seal needed to have to function properly.

I recommend doing this step outside next to a full bucket of water, in conjunction with the next step.

Now with the O rings adjusted add some Petroleum  Jelly or grease to the inside of the pipe.

It's now time to test the water gun and go have a water fight.

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