I have a Craftsman lawnmower. It has a Briggs & Stratton motor with a 'Fresh Start' fuel cap. The mower needs B&S fuel additive to run (stupid priority software...) and their special fuel cap has a little container filled with the additive that plugs into the bottom of the cap and sucks out drops of the additive as you mow.

Those cap containers, seen here, are VERY expensive for what they are and NOT necessary. ;)

I went to Sears and saw that for a 2-pack of those little cap containers, they wanted a colossal $10.99! But...I went to Canadian Tire before that and got a little squeeze tube (here) of exactly the same stuff (one tube is around the equivalent of one container) for the grand total of..........73 cents. :o I'm sure you can get them in any hardware/seasonal/automotive-type store, too.

You totally pay for the convenience of just plugging that thing into the cap rather than the back-breaking labor involved in cutting the top of the squeeze tube and pouring it into your gas can. (one tube is good for 2.5 gallons) And it does exactly the same thing. And even if I don't use all the gas this summer, it works in snowblowers, too.

Something to think about.