Old as Dirt!
Join Date: Nov 2008
Location: Tampa Bay Area
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An alternative you might also consider is steam cleaning. With a 6" inspection port, you should be able to get the hose, nozzel of a cannister type steam cleaner into the tank to blast out and break-down the debris followed by suctioning the waste-water out with a shop-vac. Given the slime accumulation, if it were my boat I would steam-clean the tank(s) and replace the water lines which are likely coated with the same slime. Chemical cleaners will kill the stuff but do not guaranty removal of the debris which can/will become the medium for future problems. The situation in your tanks is certainly evidence of why one needs to filter and treat the water brought aboard the yacht, eh?
In any case, good luck. Whatever you do, add good filters to your system!
"It is not so much for its beauty that the sea makes a claim upon men's hearts, as for that subtle something, that quality of air, that emanation from the waves, that so wonderfully renews a weary spirit."