Just replace the entire tank. Second hand milk
tanks or some other food-grade stainless
tanks can often be adapted, and I do like them to gravity feed to the engine
fuel pump. If they are not already fitted with a conical exit point at the lowest point of the tank, have a funnel made up from stainless of the same gauge and welded into place, so that NOTHING can remain in the tank, and that fuel supplied to the engine
fuel pump will always exit from the bottom only. The tank is filled by a pipe coming from just below the lid. The return line from the
injector pump can also be vented into this tank. If the top is removable, it will be screwed down on to diesel resistant gaskets. If the top can be removed--fit bafflers to the tank from
stainless steel sheeting, fitted and screwed together, and welded at intervals to the sides of the tank
Now, if the tank has a welded-on top, the inspection port needs to be wide enough to allow a length of stainless tubing, about three to six inches (8--15 cm) diameter, and you will need as many of them just a little shorter than the height of the tank, as can be stood honeycomb-like on the lid. Cut a small V in the bottom of each tube.
Reaching through the inspection port with a tube, push it into a corner, and so on, working from the outside towards the inspection hole, putting these baffle tubes into the tank until the entire tank had been baffled. If you can remove the entire top of the tank, a more conventional surge baffle can be made up. If not, then you will find the tubing works OK.
I like to have a glass visual gauge fitted to the tank so I can see the level--and this gauge needs to be screened against accidental damage. Clear fuel hose works OK--but I do not trust it for a large reserve of fuel, because this clear hose can become brittle over time and fractures easily once it has done so.
That is it. The tank will never have pockets where stagnant fuel can remain. It will not have cost you an arm and a leg--any quality stainless 316 or better tank can pretty much be adapted, and sometimes small baffled stainless fuel tanks can be acquired from military surplus. If cost is a problem--simply use a diesel tank acquired from a truck wreckers. They are not usually designed to fit neatly against a bulkhead though, and they are seldom of stanless
steel, but they will get you back to a home port in a pinch.
If one wishes to do so, it is OK to run a fuel
pump 100% of the time into such a tank, pushing it through filters from the main fuel tanks usually located at or below below engine level, and exiting back to the main tank from an overflow of the day tank, so that the "day" tank is always full. In this way, if extra filters are used--all fuel gets "Polished" and no stale fuel ever remains in either tank.
A breather for this tank can be fitted and taken well above
deck level and through a
safety filter. I use a piece of
stainless steel tube with a screw-off end, to which I have fitted brass hose fittings. Inside the tube are stainless
steel scouring pads-the sort with NO SOAP. Air and fumes get out--they are flame-proof, and no insects can get in past the pads.