If you go to an Evinrude dealer, and buy a fuel connector with the Johnson Evinrude name on the package, you’ll be good to go. Try to find a good used older tank or a new old stock one with a vent. The demand valve you are asking about is intended to prevent the engine from flooding due to excess pressure in the fuel tank. When the engine starts and runs, the demand valve opens to allow the fuel to flow. All of these extra parts are required on the current EPA approved portable fuel tanks. If you find an older tank you can save money and avoid a lot of problems, and you won’t need the ”demand valve”. Unfortunately, the older tanks with a standard vent are no longer being manufactured due to EPA regulations. Here’s a new style [current tank] with the demand valve.http://www.partsmate.net/Mercury_Quicks … oC8Ozw_wcB