One vinegar treatment (use only distilled white vinegar, NOT cider or wine), left in only an hour, is enough. The most important thing in preparing for extended layup
is to THOROUGHLY flush out all the plumbing--including the overboard
discharge pump--and the tank with plenty of clean fresh water
To rinse out the toilets, disconnect the intake line from the thru-hull...stick it into a bucket of clean fresh water
to which you've added a quart of vinegar...flush the whole bucketful through the toilet. Two toilets, one bucketful each. An hour later, another bucketful without the vinegar. Since the boat will be on the hard
, you can leave the inlet hoses off the the thru-hull till you get back if you want to.
Assuming that the tank is plumbed to a deck
pumpout fitting, even if you never use it, it's actually fairly easy to flush out the tank. Put about 6" of water in the tank VIA THE DECK
FITTING--'cuz that sends the water into the tank at the bottom to stir up any sludge...pump that overboard
. Repeat...repeat...till you're pumping clean water. In fact, you can even just stick a hose--NOT the same hose used to fill your water tank!--into the deck fitting...let the water run long enough put several inches into the tank, then start the over board pump while the water continues to run. You'll leave an inch of water in the tank...add a normal dose of your tank product.
Backflush the vent line...you're done.
When you return, backflush the vent line again to evict any critters that took up housekeeping in it...put a tablespoon of mineral oil
into the bowl with your first flush.
Depending on the age of your toilets and how long it's been since they were rebuilt, you may want to consider doing that...rubber and neoprene don't profit from sitting unused and dry. If your overboard pump is an impeller pump, be sure to bring a couple of spare impellers back with you...and use one of 'em as part of your recommissioning.
And you should recommission your potable water system when you return...I've posted directions here for doing that.
Have a safe trip in both directions! Give me a shout when you return to the boat if you have questions during recommissioning.