I have two unused tanks in my garage to show for it. just gota decide which to use and where to put it.
Based on your signature block, your riding a GL-1800 and it is easy to cut and bolt together a mount that will attach to the Pillion hand holds. I used the photo of the bracket that
Greg Rice has on his webpage to make mine. It is very easy to remove and reinstall as needed. I, however, did not drill into the tank as he did. I'm not that brave. Greg's way you
must have a shut-off valve between the Aux tank and the main tank since the Aux tank is higher than the vent in the main tank. With the valve open, gravity will cause the fuel to flow from the Aux tank into the main tank and out it's vent. You
must keep the valve
shut until you have consumed more fuel than the Aux tank holds. Depending on the size of your Aux tank, you will need to wait until your fuel gauge indicates 1/4 or possibly 1/8 of a tank. Only then can you open the valve between the two tanks. The fuel in the Aux tank now fills the main tank. It is quite satifying to see your fuel gauge moving toward full as your driving down the road. You
must shut the valve to refuel.
I plumbed the Aux tank in via the vent of the main tank. Then I plumbed the now removed vent hose onto the Aux tanks vent. This puts the fuel systems vent above both tanks and back into the bikes emission system. Fuel in the main tank will be replaced from the Aux tank, ounce for ounce, as it is consumed. Your fuel gauge will indicate "Full" until you have exhausted the fuel in the Aux tank. Then it will work as usual. Even though plumbing it my way does not require a valve between the tanks, I highly urge you to install one for safety reasons and the ability to remove the Aux tank without it having to be empty. If you don't have a valve or decide not to close it, you must fill the main tank first, put it's cap on and then fill the Aux tank. That seems easier to me than remembering to shut and open valves.