There is an air gap in tanks so that you do not over fill. This is for expansion of the gas because things expand and contract when its temp changes. Go fill your tank to the brim ontop that hot motor, and park it in the sun. so it expands more. Do you ever wonder why a gas can has a pop off top because it has to release the pressure. Your gas tank does not have a pop off valve, only the gasket on the cap. The air in the tank can compress when the fuel expands and contract the liquid ful cannot compress so some thing has to give. If you dont have air how much pressure can that gasket take before the gas is push past it and onto your bike. You may get by 100 time but what happens if it does overflow onto your hot engine.
Something else to think about, have you ever seen a gallon of compressed gasoline catch on fire much less 6 gallons.

 

If you fill to top & park it - expansion will push fuel out your overflow & garage will smell like a fuel factory...

 

Fill mine to the top every time. I also have a center stand that allows me to put 1/2 gallon more in. Of course I don't fill to the top if I am heading to the barn, due to the expansion issues, but it's not an issue if you are going to put a few miles on first.

 

I always top mine off while it's leaning on the sidestand. As soon as I stand the bike upright, I get a little burp of air to the fill neck and it leaves more than enough room for expansion. I've never had a problem with this method.

 

Fill mine until there is a tiny bit even in that little cup.

 

If I'm traveling any at all I "burp" it (shake the handlebars), and refill it at least 3 times to get all the fuel in I can. Never had any problem.

 

everytime I try and fill it to the brim the nozzle shoots out the gas a t 100mph and it gets all over the tank and runs onto the engine, sucks ***

 

Never thought about burping it! Good idea!

 

Always fill to brim when on sidestand, never a problem. Told this it the best thing to do to stop anything drying out and prevent rust in tank when leaving in storage for extended period

 

No issues here since I can never afford to fill it to the top.