Question About Gas Tank Venting/Leak

The last couple of times I went for a ride and parked my bike, I noticed a gas smell in the garage. This last time I came home and parked it I noticed small splash marks around the gas tank filler area on top of the tank which tells me gas leaked out while I was riding. I must admit I may have wheelied a time or two. I lifted the gas cap and noticed a threaded hole that looks like it should have a screw or plug in it. I took a pic for reference...

Should something be in this hole? I also checked the surrounding allen head bolts and a few of them seemed slightly loose so I snugged them up. Could that be the source of the leak, or is it related to that empty threaded hole (arrow indicated)?

This is the first question I've had to post on here since I've been able to find everything else in the archives. Great Forum!...

Thanks...

Nothing missing from the top but the threaded hole takes the overfill spigot and pipe from the underside - stick your finger in to see whether this has become disconnected (unlikely) - the pipe internal to the tank is connected to the external spigot and external pipe under the tank front rhs - check that this external pipe and the one to the rear lhs under the tank (vacuum vent) isn't pinched/kinked - another possible cause is at the cap itself - search for the respective thread(s) here - some of us have removed/modified the tank vacuum vent connection at the cap - was there a hiss of air when you opened the cap?

Thanks for the info. Now that you mention it I did hear a slight swoosh sound when I lifted the cap...

I'll lift the tank and check the hoses next time I'm in the garage tinkerin. I didn't notice any more leaking after I snugged the bolts and went for a ride...