Always bothered me that the Magpul vfg had a cavity in it but no way to store things inside the way you can in most pistol grips. Well no longer! Here is a fully 3d printed, no-hardware, solution that creates a suction seal to store batteries, parts, oil, or Apple air tags (check out my other uploads for capsules).
The o-rings are printed in TPU and the press fit is almost impossible to remove without a set of needle-nose pliers (this is a feature, not a bug). Pliers should be a part of your kit by now to clear malfunctions.
The plug makes an audible pop sound when being removed so I'm going to call that “water resistant” - If you do try it out underwater, leave a comment to let us know how water resistant!