There are different "school of thoughts" on the wiring, hoses, and whether to empty the tank.
DEFINITELY disconnect the battery, regardless.
It's completely possible to do it with a relatively full tank. I've done it both full and empty. And draining the tank is a pain.
One of the arguments in favor of doing it with the contacts immersed is that sparking is less likely if the metal parts (pump terminals/socket/screwdriver/whatever) are submerged. Additionally, there's no oxygen when immersed, so tapping metal bits together unexpectedly shouldn't result in combustion.
If you drain the tank, unless you
really drain it, so it is
dry, and then blow the fumes out with compressed air, you're still going to have gas fumes, plus oxygen, in the tank. These can ignite if you whack metal things together and create a spark. A nearly-empty tank is arguably less safe than a nearly-full tank. Draining it
dry and blowing out the fumes is certainly the safest method.
Logistically, I rather prefer to make most of the connections in the tank. Wiggling things around with hoses attached seems much more awkward for me. Doing it in the tank also means I ensure that the screws on hose clamps are positioned to be accessible, whereas if I attach things outside the tank, I may end up putting the hose clamp screw in a place where I then have to remove the part again to access the hose clamp. The pump wires on mine are plenty long enough to rest the pump on the outside of the tank without disconnecting them first, so I do tend to leave them connected.
I use a 1/4-inch socket and a thumb wheel attachment inside the tank. (Like this:
http://www.sears.com/craftsman-finger-grip-socket-adapter-3-pk-/p-00943401000P?PDP_REDIRECT=false&s_tnt=39869:3:0) All the hose clamps on the bike that I know of use 7mm screws. The terminals on the pump are 7mm and 8mm.
