I think Blackheart is running the aux tank first then main then reserve. That's how I'd do it.

 

The Auxillary tank should ALWAYS be run first until it is empty. That decreases the length of time the extra weight of the fuel will be affecting the subframe. After the aux tank is drained, switch to the main tank, and shut off the aux tank (easily done while riding...don't even need to stop).

 

I was out fire road riding near Grizzly Flat this summer and I chanced upon a guy riding two up with his wife on a KLX. By the looks of her she weighed a lot more than a gallon of gas... poor bike . But the subframe seemed to be able to take it, at least for the time that I saw them.

 

The KLX250 subframe I saw reduced to trash had a gas container (about a gallon) that was mounted to a rack on the rear. Miles of whoops caused the subframe to give up and snap. If you aren't getting quick changes of verticle direction, I bet that subframe will hold a lot of weight. But, it's not built to withstand much weight under the commonly experienced forces of riding off-road the way "normal" off-road riders tend to operate.