Gas leaks when pumping gas

Gasoline leaks when I fill up the tank for my 2009 Taco. Only leaks when filled up. I do not top it off. Doesn't leak when truck running nor does it leak on inclines/declines standing still. Again, only when filling up. CEL has come on (as expected since I have a leak some where)

Leak seems to be coming from top area of tank. Possibly the fill tube, maybe the vent tube. Not sure.

Since it is such a PIA to drop the tank, how can I figure out which area might be the culprit of the leak (other thank filling up tank and watching for the gas to leak out)? Is there some smoke test that can be done? Maybe blow smoke into filler pipe and see where it comes out? I have searched all over..found some videos of dropping tank and etc but haven't found a good source on how to find out where the leak is coming from.

 

Might be an issue with the evap system. I'd check that first.

 

a variation on a smoke test: force smoke down the fill tube and see if it leaks out the tube and/or the top of the tank