My boat has a single aluminum fuel tank
holding about 690 liters. I had never even seen it until recently - it lives between bulkheads and is buried under joinery - you have to either take apart a bookshelf or remove the built-in microwave to get to it.
I had the tank cleaned out when I bought the boat 3 1/2 years ago and will do that again this spring, but it bothers me that I can't check the tank for water
and grunge. There is no sump or drain.
I suppose I could make up a long rigid plastic or copper pipe with a bulb on the end, and suck a bit of fuel
from the bottom of the tank through the inspection hatch
from time to time. What do you guys do?