Sucking the fuel out

[Sasquatch Jim]

 Or just remove the cap and hold the bike upside down.  This technique is difficult to use on your pickup truck.

[redhawk47]

I use one of these: http://www.aerostich.com/e-fill-siphon.html
Packs small on the bike. The case is a container to xfer fuel to your buddy's bike. Has a shut off also.
Works great for emptying the tank before removing it.
Dan