Im assisting a friend whose correcting survey deficiencies abd his
purchased motorsailer. Among the usual long list of such items is a 45
gal Al MSD (holding) tank nicely custom-fabbed & fit by a former owner
(why Al??arrggghh) to perfectly fit its turn-of the-bilge space.
Tank is also parellelogram in plan, i.e. any reasonably avail polymer
tank which may fit the space will be of lower capacity. Tank has a
small lkg IWO a vent o-let, and a 10" handhole. Owner's yard had
ordered a new bladder which I'd dissuaded him from following through
with (thank for your years of debunking them & correcting me then too
Peggyg), but R/R time window is short (5 days). Al tank will be
pried out of its foamed-in place position via the usual Chinese
firedrill that requires in AM, & taken ashore. We are contemplating
the *option* of cleaning the tank, assessing its condition, and if not
significantly wasted, welding and/or doubling the leak, blasting or
otherwise prepping it's insides, and coating it with an appropriate
epoxy or other suitable coating in order to exend its service.

Experienced or hands-on guidance re a specific coating and/or other
repair & protection option I may not have considered?

Much TIA,
Frank