When you open the side Gobi. you will see two circular rubber plugs. pull both of them, one to fill and the other to vent and speed up filling. This will only really work if you buy the fuel petcocks and mount them to the front of the bags. The o-ring that comes with it is trash, get a thicker o-ring to seal it. Yes it is a pain in the ass if you in a hurry. but if you want to have an extra 2 liters of water or jameson per bag and dont have much space then this is the trick.
And I do like the Gobi's a lot. The aluminum panniers look nice and all but Im not comfortable with those with actuall off roading. the gobis may crease a little and have some skuff marks but still work great and are able to open and close at the end of the day. plus mine came with the bike
. And if you do plan on wheeling with panniers carry two ratchet straps that are about 1" 1 1/2" thick. So if the latch breaks those will hold em on. or you can strap broken parts to your bike, or tow your buddy if need be, or to throw in a truck or trailer if you break down. Ive needed ratchet straps for all of those scenarios.