unless you like the drilled drain plug with a cut of copper tube pushed into the screw, here's lot faster and just as good method. check them all at once.
get some aquarium clear tube, medical, oxygen breather tubes.
4 tubes different lengths, give yourself enough length to tuck up under the choke lever.
light a candle before you drain any gas and a fire extinguisher nearby and however long say #1 is gonna take hold the line over the flame not real close but rotate the plastic until it gets rubbery and pull slightly until the taper narrows to about the size 5 or 6mm and hold it until it cools. cut that right in the center of taper. if it's still warm it'll have a tendency to retract, if you roll it over the flame too long it'll collapse.
go down the line to make cut however long #2 is gonna be, and do the same for 2 more cuts for #3 & 4 carbs long, heat and make the taper first.
put the candle out. and shut the petcock off.
drain the bowls 1 at a time into a cut cola can about an inch high, and look at the gas in the can for dirt or anything other than gas if so don't run it until you fix that.
as long as the tube isn't pliably hard from uses before and gasoline (they last a few months,) push the taper into the drain hole and barely press and make a turn, 1 or2 turns and it's self sealed, and route them up to the side your working on. if it's checked out, shut the gas off. and use the coke can bottom drain the tubes. 1 at a time, keep an eye on what's draining out.
