First make sure the hoses need replacing
If they don't stink, they're not the culprit.Nor is your holding tank likely to be unless it's leaking--which is possible if the tank is aluminum, but not if it's plastic. Otherwise, it's just about impossible for the holding tank to be source of odor INSIDE a boat, 'cuz odor from inside the tank has only one place to go: out the tank vent. Odors are always strongest at their source...yours is strongest in the aft cabin...so what's in that area? Y-valve? Macerator? Both could be leaking slightly. Or, it could have nothing to do with the sanitation system...a wet bilge in major need of a real cleaning, a dirty sump, or trapped water below the cabin sole can smell like a sewer. So before you start pulling things apart and replacing 'em, you need to find the source of the odor...otherwise you can spend a lot of money you didn't need to spend and do a lot work you didn't need to do. The link below may give you some help.