Tank Drain Plug: fuel screen clogged with varnish

Tank Drain Plug: fuel screen cleaned and restored

This is a pre-filter. It is intended to protect the fuel pump and fuel lines from large debris — trash that might have fallen into the tank during refueling. There is a baffle in the lower part of the tank, a false floor, creating a collector. The plug has dual threads. The top set of threads seals against the bottom of the main container. Fuel enters the screen and exits an orifice (below the top set of threads) and into the collector area. Fuel is drawn from the collector by pump.

Ageing gasoline eventually  blocked this screen effectively choking any and all fuel flow. And, this is the reason why the engine ceased running. Its discovery was an ah hah moment.