For those of you with a nipple on the bottom of the float bowl.

Connect a clear hose to the nipple and run it up along side the carb.
I put a block under the kickstand to bring up near vertical like when I check the oil level.
Then open the drain, the gas should flow up the hose and it may stop at the top of the bowl.
Set the petcock to prime and now the gas should come up to the top of the bowl.

For those of you w/out a nipple there's another way.
This might be easier with the carb off the bike, but could be done on as well.
If you take the carb off the bike, I found it will sit in a coffee can just right.
So find a can that all four ears of the bowl sit well w/out tipping.
Take the gasket off the bowl and replace the bowl back on the carb.
I use a MixMizer (wallyworld) to fill the carb, pull out the plunger and it comes with a tube that fits on the carb just fine. Pour gas into the top and the the carb will fill with gas till the float shuts it off.

If it's overflowing the bowl, the floats are set too high, adjust and repeat.
If it's at least trickling out, raise the float level (or lower when it's upside down) till it does.