No need to remove a perfectly good polyethylene tank in your Pearson. Its polytheylene but may need to have the bulging cradle reinforced on the sides .... but thats a structural problem. Being polyethylene, the tank is pretty much chemically inert and will withstand chemical cleaning with the most rigorous chemicals.
To clean the tank (in place) mix a diluted solution of lye or other stong caustic and water. The lye will **dissolve** all the bioburden growing in the tank. Lye is quite dangerous to use and will cause chemical burns that are very slow to heal - so if your not comfortable about using lye you might contact a dairy supply house and connect with a dairy tank cleaning service; otherwise, be sure to wear heavy rubber gloves and chemical grade goggles. Read all the warnings you can get your hands on regarding "lye" and caustics. Fill the solution so that the tank is completely filled ..... and the level is *** well into the vent*** line
Let the solution soak in the tank for several DAYS or longer. The solution will dissolve all the mold and mildew cells. (Dont waste your time with Chlorox or Peroxide. Chlorox & peroxide are used to sanitize a ''clean'' tank. What you have is a ''slimed'' tank. If you can see the growth you have more than a sanitization problem and you need to remove the cells. Chlorox or Peroxide will kill/stun the cells but wont disolve them. ) After the soak period, put a gallon of vinegar in the bilge. Break (cut) the hose connection at the tee under the basin in the head near the seacock (in the alcove on the starboard side near the sole) and let the solution drain into the bilge. When the tank is about half empty pump
the neutralized solution overboard. Dump in another gallon of vinegar and let the remaining half tank fill the bilge, when the bilge is almost full, pump
overboard. What you will pump
overboard is a chemically neutralized solution of water and ''salts''.
Fill (over fill) and rinse the tank several/many times (at least 4-6 times) to be sure to dilute any lye solution that remains. After you fill rinse many times you can ''be bold'' and ''taste'' a few drops the water on the back of your tongue.... but if it has ANY perceptable ''bitter'' taste rinse several more times.
Then replace EVERY hose from the tank and the rest of the water system (easy on a P30). If the hose is original the mold and mildew will have penetrated almost through the hose - brown color. Especially replace the entire vent line
.... you will find this on the port side of the tank, under the vee berth surface and runs forward into the ''chain locker''. You will have to unscrew the plywood ''floor'' over the tank to get at the vent line
. The vent line
will terminate an inch or two just under the deck on the forward/port side of the chain locker bulkhead ---- remove and replace the entire vent line.
What is continally contaminating the tank is mold and mildew GROWING in the vent line. Every time the tank is drawn down the mold growing in the vent line will aspirate spores into the tankage. For the new vent line cut a hole just in front of the head/vee berth bulkhead and another hole in the overhead alcove on the portside. Run a new vent (3/8" dia. is fine) from the tank, along the hull side and into the portside alcove above the vee berth. ****** IMPORTANT: to keep mold and spores from growing in the new vent line in the future, either tape a large fist sized wad of ''bandage gauze'' & "bandage cotton" or put a bacterial grade hydrophobic commercial ''vent filter'' on the open end of the vent line. A 50 mm dia. commercial 0,2uM "Vent filter" with 3/8" hose barbs will be sufficient. You can get one of these from companies such as Whatman, Millipore, Pall Corp, etc. or one of their distribuitors. This vent filter will keep the tank exponentially cleaner by preventing mold/mildew spores from entering the vent.
Keep the gauze dry and replace the ''wad'' twice a year.
Replace ALL the old water hose, then shock sanitize the 30 gal. tank with either a ''heavy dose'' of Clorox or H202 (drugstore grade).
The original hose that Pearson used is very porous to mildew/mold growth - most of the hose will have turned BROWN --- all the way through the hose wall! If you dont remove the hose the mold/mildew (filaments) growing IN the walls of the hose will recontaminate the whole tankage all over again. I''d like to be there when you see whats growing in the that vent line! Its going to turn your stomach when you see the goo that lives there..... and this is what''s continually recontaminating the tank. Replace the vent line and terminate the open end of the vent into a ''clean'' area (such as the ''alcove'' above the vee berth).... and put a ***vent filter*** on the open end.
Hope this helps. If you need additional info email me direct.