Re: 6 gal. Johnson fuel tanks
The best fuel guage is your wrist.
But I don't like running out and it can be dangerous if you have bad timing--in a channel, at a dock, in an inlet or near a dam or other hazard. So I check them before I start a leg of the trip that might encounter such, or a long stretch on a plane at a good speed; the sudden slow down can jolt a passenger or cargo (and thus the rule against people sitting on the gunwales or worse, hanging their legs over the bow).
