I dropped my tank (also a YJ) some months ago to clean out, so I have a pretty good picture of how that looks like still fresh on my mind...
You will find 4 hoses down there: the filling hose, the return hose (these two are connected to the filling cap) and 2 vent tubes. When I put the tank back up, I also had a gas smell fill the Jeep (in this case, it was 100% my fault, as I forgot to tighten the bands that make sure the hoses are tightly connected to the tank!), but I also noticed that the venting hoses were not in any kind of good shape, so I replaced all hoses at this time.
The two vent hoses will connect to each other with a T connector, and then go up to behind the rear left (driver side) panel. You can more or less access the filling hose and the return hose by removing the gas filler neck, and the plastic mud protector that's behind the rear driver side wheel. It's not easy, but it can be done (I did the 20 gal conversion this way, and this required removing one of the 2 hoses).
My advice: change all the hoses if you can. With a hidraulic jack, you can drop the tank, change the hoses, and put the tank back up in about 2~3 hours. Just be adviced that putting the tank back up will require some pushing to make it go over the exhaust (so make sure the exaust pipe is cool). While you have the tank droped, you may want to also change the sending unit's gasket; mine was less that $20 (dont remember exactly how much) at the stealership...
Felipe