ps i forgot to mention,,make sure that tank has been rinsed out thoroughly before assembling the stopper,and whenever filling let a little fuel flow from the pump first ,incase dust or grit  got ,is in there from prop blastting junk at the field ,before connecting to your tank,,i agree with joe neoprene disintergrates,,incase youre confused,,that little screen shown in the pics above is found in the carb,,once junk gets that far,it causes your to dissemble and clean ,,its weird how our weed whackers never clog up ,but they have a big filter that takes alot of junk before they clog up too.