The Eight.3 Vented Valve Plug is designed to burp extra air out of the bag --- more water = more weight.

New for this year, the Eight.3 Vented Valve Plug is a direct replacement for the Eight.3 Bag Plug, but it also allows you to burp excess air out of the bag by loosening the fitting. Spillage is minimized and you don't have to worry about removing the fitting completely from the bag.

This is perfect if you are trying to get the maximum amount of water in each bag.