T&T: fuel tank question

[badornato]

i just bought a 85 krogen 42 and the old owner told me he always kept
the fuel tanks "pretty full
down in the engine room the sight glass tubes are full to the top on
both sides...so how many gallons do you think i burn till the sight
tubes show a level..?
are people putting biocides in their tanks in the winter..?
do most people keep their tanks full?
if i am not cruising and just using the boat for day cruises, and
using it perhaps 200 hours a year, how should i manage the fuel?

-- 
bruce t adornato
krogen 43 amelia
san francisco