Hoses--not all, but some, especially the inexpensive single walled flex PVC--can definitely become permeated with odor and it sounds like that's the source of your odor. And yep, there's definitely a hose that runs from the toilet to the tank...another one that runs from the tank to the deck pumpout fitting, and a third smaller one--the vent line--from the top of the tank (or a side or end AT the top) to a thru-hull (USCG regs require that all waste tanks be vented the OUTside of the boat).
At the risk of being accused of shameless self-promotion (people who've been hanging out here solving problems for 20+ years are allowed to get away with a little of that once in a while)...I have to agree with Dave's recommendation to buy my book--which not only deals with every source of odor on a boat and how to cure, or better yet PREVENT 'em, it's actually a comprehensive "marine toilets and sanitation systems 101" manual that explains the laws, describes all the types of systems and how they work, and will help you learn how to operate and maintain your system to prevent 99% of problems instead of having to cure 'em. 'Cuz you get to do any preventive maintenance on your terms when it's convenient...the need to cure a problem never happens when it is! And I'm always glad to answer any questions it doesn't--or even the ones it does.
It's always available from the sbo.com store (see link in my signature below), but they've just begun offering signed copies for the holidays...order your book(s) from sbo.com...they send me the orders, I sign and mail 'em from my office.
--Peggie
