I do not know as well your intentions, though why don't fill this jar by gasoline and when your car stops use stored in gasoline for mileage increasing. Sure it's easiest way :).
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Yes this link would have a sense for post topic. But what we need to do with mentioned jars. Sorry for my poor language. It seems ours Guest had no time for a while to make his/her ques more clear.
My dad tried this with the family car when I was growing up in the 60's. Vacuum gauge on steering column with a jet type valve, tube running through firewall to a big jar on the transmission humo. Noisey! He claimed a little improvement...