Permeated sanitation hoses are only one of the common sources of odor on a boat. Bilges in serious need of a real cleaning instead of just dumping some bilge cleaner into 'em,, adding water and sloshing it around can make a whole boat smell like a swamp or even a sewer. Shower sumps in need of cleaning can make the head stink...dead and decaying micro sea life in toilet plumbing are another source of odor in the head. The chain locker is prob'ly the most overlooked source of odor...the same micro sea life that makes toilet flushing stinky (mostly limited to toilets that use sea water) die, decay and stink if they aren't rinsed off the anchor rode. And then there are the oil or diesel drips and spills that contribute odors of their own. The most UNLIKELY source of odor is the holding tank, unless it's leaking 'cuz odor from inside the tank only has one place to go: out the tank vent.
Each source of odor has its own distinctive odor...bilges and usually smell like a swamp, permeated sanitation hoses usually have a combination sharp chemical/sewer odor, mold and mildew are easily identifiable. The good news is, they can all be easily identified. Curing them almost always requires manual labor.. prevention is easier. I'm gonna do something I rarely do in a forum: suggest that you buy--and READ--my book (see link in my signature below). It not only deals with every source of odor on a boat and how to cure, or better yet PREVENT 'em, it's also a "marine sanitation systems 101" manual that will teach you how maintain your system to prevent problems. 'Cuz you can do preventive maintenance when it's convenient...the need to cure a problem rarely happens when it is. And I'm always glad to answer questions.
(end of shameless self-promotion)
--Peggie