I think you need to look at basics at this point. Hopefully i'll get this right (I just got off a cruise ship last night). On all non-CA bikes there is only one tube in the rear of the tank. It is a steel tube welded in that goes up the inside on the tank to the void under the gas cap that drains RAIN water and spilled gas (overflow) out the rear of the bike. The gas cap has a red (or black) one-way diaphram in it to allow atmosphere to enter the tank thru air passages as the fuel is used so a vacuum is not created. This is how water condensation is also accumulated over time in the tank. It can clog and also create a stall condition when it makes a vacuum on the tank. Under pressure, this same vent squeals (or "sings") as it relieves pressure. In your case, it sounds like the fuel level is so high that it is pushing fuel out, and probably will continue until the level drops.
The other issue you may have created by linking the two hoses (not capping) and then overfilling is that the gas vapor return tube (CA stuff) is below the fuel level and under heat pressure (developed as the bike warms up or simply cold fuel from underground warming up) it is then back feeding up the other vapor vent line and filling the void under the cap. Cap these two tubes (securely) and the condition should not exist anymore when the fuel level drops.
In my picture (non-CA) the yellow arrow is pointing at the gas cap anti-theft screw. The other "open" hole to the the right is where CA bikes have a rubber plug pushed in I think.
If i'm not right, please send me back to the cruise ship please.
