If the tank IS vented inside the boat...
That must be corrected ASAP!'CG regs require that all waste tanks be vented to the outside of the boat because methane is flammable and the anaerobic gasses generated by waste breakdown--sulfur dioxide and hydrogen sulfide--are not only toxic, but can be lethal in high enough concentration in an enclosed space.So check that out first.The hoses MAY need replacing. To find out, wet a clean rag in HOT water...wring it out and wrap it arouond a section of hose. When the rag has cooled, remove it and smell it. If you can't smell anything on the rag, the hose is fine...but if you can smell the same odor on the rag, the hose has permeated. Replacement is the only cure. Test each section of hose...use a clean rag for each section.Whether the toilet should be replaced depends on its age and the make/model...unlike household toilets, all marine toilets are NOT created equally. There's a wide range in their quality and durability.... Iow, you get what you pay for, and most builders--most owners too--don't want to pay much.So what's the make/model of the toilet? Or, your odor problems may not have anything to do with the sanitation system...there are many other sources of odor on a boat that make it smell like a swamp or a sewer. You asked if there's a manual...try the link below.