I supervised an FIM World 24hr Endurance
record and one of the modifications they made was to fit a beautiful aluminum extra fuel tank on the rear hump in the low pressure area behind the rider.
It was not very large and only weighed slightly over 8 pounds when full.
They just put a T in the supply line and vented the tank forward to the area behind the fairing.
The result was the tank never drained until they were stopped and made the bike handle so bad on the 5 mile circle that they rode it 1 handed to limit the natural feedback from the rider that is always late.
Not until a crack developed in a seam did it empty onto the riders back did the handling improve and it got even faster when the took the empty tank off.