Or what about that lady on Father Ted? She might do a good job and if you put the lid on you wouldn't hear her going on....go on...go on...go on.............
Probably best to flush out w/water a few times until water is clear, empty it and add some green stuff with a little water to keep it freshish over the winter.
Unless you plan on removing and thoroughly cleaning out your tank and then ensuring that it is bleach free, you should NEVER use bleach in a holding tank. A holding tank is like a mini cess pit and works by the healthy action of bacteria. There are 2 types of bacteria involved, aerobic and anaerobic. You must have aerobic bacteria and anaerobic bacteria is what causes the smells. You can buy products to kill off anaerobic bacteria leaving you with a healthy system. Bleach will just kill them both and once the bleach smell disappears you wll be left with an ever increasing stench. I know some sh*t.
Try http://www.boatsafe.com/nauticalknowhow/phall.htm it has all you ever needed to know about sh*t in an article there.
"I am the master of my fate: I am the captain of my soul."..........I think????
I have fitted a holding tank and treat it like my sceptic tank at home. Use it and add a dead rat/rabbit to the tank to get it started with nice aerobic bacteria - no smells.
Or flush it well through with lots of fresh water and add some dishwasher soap once it is nice and clean. Or take the top off clean it out completely and add fresh water to completely fill it (MAKE SURE NO FROST EXPECTED).