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Something like this: https://www.ebay.com/p/1427138908
That is not a double line. I had Mercury engines/Mercury built engine...Wizard 25 hp back in 1959 and had them off and on ever since. Never had one with a double line.I took a look, I'm not sure. The dealer told me it was a double line, one sucking gas and one as a return from the motor pushing air to pressurize the tank.