Great info here on this thread.
About 5 years ago I went on an amazing trip through Utah and Nevada with some other 80 series cruisers. One of us had an auxiliary tank. Guess what, he could only go as far as the guy with the least amount of gas. That was an interesting observation. We chatted about that around a camp fire. Basically he said it's great and loves it, but really it's only a benefit when he is solo. if he is with a group, there's no advantage to him if everyone else is running out of gas.
The entire trip the rest of us were hauling jerry cans and dumping them in on occasion, but he was hauling more water and food!