Not a good idea. Open gas cap. Note the hole to the left of the filler hole that is recessed deeper in the tank. Clog that and water empties into the gas tank with a simple lift of the cap.
So you don't want to clog a hole on that left tube at either end. That remains open just for that reason is how that cap assembly fits on a tank. See that idea right down the drain? Forget that idea on the weather "vent." Forget washing the bike too.
Again, we have come full circle more or less.
A. A new tank is still the option.
B. The hose up the vent tube and piggy the 14.7 was more a demonstration about vent-vent-vent.
C. The only out is an old style type lawnmower cap that is one hole and the air moves both ways.
If I were to test the OE gas cap, I'd plug up the right vent with a gas resistant rubber nipple plug from NAPA or a boat store, something made for gas/marine grade type rubber, etc.
This is the scary part so either the bike feels sluggish, or the tank implodes you do not top it off first. Harder to squeeze liquid than air, right? That's the quick test.
Then step to scary part two. What happens you drain the tank and not a thing happened as if normal was the ride with full power at the throttle, etc. Now, sit the bike in the hot sun with about a gallon of gas in it. If the OEM tank cap flaps that diaphragm like blowing into a rolled up paper party noise maker, you lucky dog you; was one rubber baby buggy nipple bumper upper and over the vent tube is problem solved. Not how I'd approach it, but you are on your own with the decisions you make.
Tormenting the motorcycling community one post at a time