What Mark said makes sense.
Does it ever happen when you have a full tank?
IF it happens more, or less, dependeing upon the fuel level, it must be inside the tank rather than outside it.
__________________
BroncoJoe19
2006 Alt Fuel Jeep (electric)
'98 windstar 3.8L
'99 Crown Vic 4.6L
'90 Full Size Bronco 5.0L
I'm not a professional mechanic, take my suggestions with a grain of salt, or a cup of coffee 
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