In the Peoples Republic of California we've got these POS vapor recovery foreskins that limit the volume you can get in the tank. They work on a automobile gas tank with a lengthy filler neck. But are a PITA on a bike. You can try to pull the foreskin back with one hand so you can see if you can fill the remaining volume without squirting yourself in the face while holding the nozzle with the other. These devices free up one hand so you can hold the nozzle and still look into the tank.
Some of us have bikes with marginal tank volumes like the Transalp, so I like to get the tank as full as possible. Many of my older bikes have a hump in the middle which prevent proper insertion of the nose into the tank. No fuel will flow unless you compress the foreskin.
I like his take on the idea and wish the creator good luck.
XLV750, RTL250S, 1989 XL600V, 1990 XL600V Transalps Red and Moonstone, 1992 XL600V Green, 1993 CRM250R, 1994 XRV750 Africa Twin
2009 FE390 tagged, 2011 FE450 tagged, 2011 FE570S super motard, 2011 FE570S