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It doesn't actually appear to be crimped, but looks to have a rubber tube bent over and tie-wrapped over it. The drawing doesn't actually show it, per usual, but shows #18 as the vent hose. It is there so that if the tank overfills, the excess will drain to the ground; also, if the vent is blocked, a vacuum can form in the tank, slowing or stopping fuel flow. Since that tank has a vent from the bottom (which has an internal metal tube reaching near the cap), the cap won't have a vent hole, unless someone replaced it with one that does. Perhaps that person didn't know what that was for, 'capped' it with that bit of hose, and put a vented cap on.
 

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Well, it could be that the tube inside the tank is cracked or broken, and that's why they tried to cap it off. Not a great way to do that, IMO. You can test your fuel cap for a vent by putting a longer (clean) hose on that outlet, close the cap and put a short bit of fuel line between the outlets, then blow into the hose. Pressure will build up in the tank, if the cap is not vented. To test the in-tank vent for leaks, prop the tank upright outside, and add fuel, slowly. If fuel starts dripping from the vent before it reaches the top of the tank, the in-tank vent tube is leaking. A better, fuel-resistant cap on the vent outlet and clamped (not zip-tied), and a vented fuel cap would be the repair.
If it leaks from elsewhere, like the seams or around the outlets, you'll need to see about that. A seal is simple, but a leaking seam is harder. If you find no leaks this way, it could just be the hoses connected to the outlets were bad, or the tank really overfilled, either at the pump, or from the fuel expanding in the tank from engine heat. If it came from the vent for this reason, then a hose going to ground would be the answer; you'll still get fuel smell if it overfills, but at least not fuel all over the bike. Bottom line: you have to find the real source of the leak, and go from there.
 
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