There should be a drain in the float bowl to drain it. It will look like a screw and on the bottom of the float bowl there is a hose. Make sure you have that hose in a can or somethin' before unscrewing the drain screw. Don't use a styrefoam cup or it will vanish before your eyes, I found out the hard way. To drain the tank I would just pull the line off the carb and turn the valve to reserve and let it drain into a gas can. Old gas makes excellent weed killer, ummmm so I heard.
3 years is a long time. I would be willing to bet that if you havn't started it you might want to pull the carb and rebuild and clean it real good. If it runs fine now then you're probably alright. I've seen bikes set a long ass time and the carbs be ok then I've seen them set a year and the carbs be jacked up enough to need disassembled and cleaned. I would still drain the gas reguardless.
3 years is a long time. I would be willing to bet that if you havn't started it you might want to pull the carb and rebuild and clean it real good. If it runs fine now then you're probably alright. I've seen bikes set a long ass time and the carbs be ok then I've seen them set a year and the carbs be jacked up enough to need disassembled and cleaned. I would still drain the gas reguardless.