Chris, Forget what Ric's telling you he is miles of course. Assuming you are talking about this plug

It is a tube that runs from the bilge, under the gas tank under the rear double birth and finishes at that plug. As long as I had my boat I found no usefull purpose for it. Mine also leaked when I first got my boat. Make sure your bilge is dry, remove the plug, wrap some PTFE tape round the plug thread, replace it and forget about it everything will be fine.
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Beyond the Blue
"If we improve with age I'm now excellent"
Ex 1998 238 Vista 5.0Gi SX DP
Lexus RX300