A lot of good advice here, so I will avoid beating a dead horse...
In the future, I would really recommend installing a small (<5 gallon) fuel tank
. And keeping the large one empty unless you know you will be using a lot of fuel for a particular trip. This allows you to keep a relatively modest amount of fuel onboard for normal operation, and only need to fill up the big tank when absolutely needed.
This way you ensure that the fuel onboard is fresh, the big tank can be kept very clean, and since the small tank can be kept pressed (topped off) that condensation
is minimized. I installed a tank like this on my Beneteau
, and for a cost of about $100 it has been well worth it. I now fill up every two months of so instead of every two years. And my big tank is absolutely clean, dry, and free of bugs.