Here are pictures of the modification.
Be back in a minute to explain.
Okay I am back.
In the first pictuer you will see where I set back the threads and thinned the wall of the pipe.
The second pictuer if you look there is a little ridge on the MG cap this ridge snaps into the inside diameter of the bottle or in this case the PVC pipe.
The outer collar or what ever you want to call it has to fit on the outside of the bottle or PVC pipe.
If the pipe isn't thinned down enough it will crack this thin piece of the green cap as I did but it still works.
In the third picture you can see it snapped onto the PVC pipe just like it does the bottle.
Worth
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