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If using the sight gauge,  moving the tank vent to a location remote from the 
gauge vent may cause erroneous readings.  In addition, the bottom location is 
perhaps more vulnerable to blockage, especially by dirt thrown up from the 
wheel.
Another approach is to make a gravity activated one way valve from a ball 
bearing, a short piece of plastic tubing which fits snugly over the existing 
tubing, plus a couple of hose clamps.  On inversion this would block fuel 
leakage via the vent, solving the problem without moving the vent.
John      A044
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