Plumbed the bottom of the sight gauge with copper tubing. Not knowing the service life of the polyethylene tubing (though it is rated chemically as compatible with up to 30% alcohol fuel) I decided on the copper for durability. There is a manual shutoff valve at the tank outlet to the bottom of the sight gauge in case the sight gauge plumbing develops a leak in flight. Not shown in the pictures is a knob to be installed. The knob will be colored half red, half green. With the valve closed, the knob will appear red. When opened a half turn (or multiples thereof) it will be green. This is to visually check that the valve is not closed, possibly giving a false reading on the sight gauge.
After installing the copper, the manual tank shutoff rod was interferring with the tubing. Made a new shutoff rod.
