My boat was 1988 built when I bought it in 2009. There were no inspection ports
so I asked a chap to install 2 of them. When he was finished drilling the first hole he started cleaning
out the crud (I had hand pumped the remaining few gallons out of my tank). Tank was rusted badly in one corner and condemned. I installed a new tank with 2 inspection ports
I pump out my tank each year and clean it. (Just finished job last week.) This is what a mild steel
, unpainted interior
looks after 1 year--sometimes filtering the inflow but it's so slow (and boats are always waiting)--not always.
Here is a pic of the bacterial growth/sludge--the black mounds. It is slippery, goey but easy to remove with a clean scraper. It pays to have a full tank all the time as you can see from the rust line. Cleaned her all.
It's cool here in Buenos Aires so I'm running my Dickenson diesel stove and hope to catch particles that way before heading south, where one needs an engine
ps: The pencil didn't live there. Just for reference.