its easy to pull the fuel line off the tank petcock and the line that goes to the carbs, put an external fuel bottle on the pump and run fuel and carb cleaner thru it.
I would ditch the fuel filter before you do this too, and get a new one.
If the tank is not full of rust and you run the pump till the fuel comes out clear, you hit the worst parts.
BTW, the fuel pump runs when you turn the key on with the kill switch = Live. I think it only runs for a few seconds, or maybe it runs till it builds back pressure - either way you might have to cycle the key a few times to run it repeatedly.
The real question is what was done to the carbs when the bike was last used? If the petcock was turned off and the engine run till the float bowls ran dry, you wont have any of that goop from the tank in the carbs... but things could be dried out in there, possibly corroded and green, and the floats might stick till you flush some carb cleaner thru them.
If the gas was left in the float bowls it might have all evaporated out and left goo in your jets.
If it were me, either way, clean fuel tank, lines, filter, fuel pump... then with carb cleaner / seafoam in fresh gas (follow the directions, dont put half a can in 2 gallons of gas)... turn the key on, let the pump fill the carbs and see if it starts.
IF the bike will start up and run at all, you have a 50:50 chance that carb cleaner will flush out the jets and passage. It might take a good 200 miles of riding hard to get it running well, but if its running at all then fuel and cleaner is flushing thru the jets, and they might do the job,
If it simple wont start, or it only starts on one cylinder (make sure both exhaust pipes are getting hot...) or if the floats stick and fuel comes out the over flow tube and it wont stop after a few minutes... then you will have to take the carbs apart and have at it with the infamous craigslist wording "Needs TLC"