I keep a small, powerful LED flashlight under the seat. Gas hose in one hand, flashlight in the other. Squirt some , look some, etc.
There are several posts on scooter forums about overfilling a scooter tank. Gas flops about in there, runs down the vent hose which is just under the cap, in the 'neck' of the tank. Supposedly, the gas will flow down there and foul the one-way vent valve located in the hose, half way between the tank and the charcoal canister...or back into a parked scoot's carb via the siphoning phenomena, or even clear into the head to 'lock' the engine, or some such. This is all pretty scary stuff. But then so is the popularity of the Duck Dynesty folks.
As Vivo mentions every so often when we start to hyperventilate - these scoots are sold to & made for rugged use in 3rd world countries.
So, keep the tuna sandwich under your seat dry by not getting crazy with the gas nozzle - but gas it to a point close-but-below the neck....and you can do this easily with the use of your $2 flashlight.
'Course, I have one of those bars in my LIKE's tank to help me.....
and new batteries in my light.
(To calm things down - I bought a new 2+gal gas can and and a big blue funnel & do my fill-ups in the solitude of my garage.)
Stig