Smell problems

The biggest cause of smell is old hoses. Be aware that cleaning tanks or even replacing them is not the cure. All the hoses have a life expectancy.
Track them down, remove them from the grey/black water tanks, make sure there are no leakages and then treat the tanks.
Rarely is it the tanks themselves.
Cheers,
Kafue

Depends on the smell. Indeed aging hoses are a common issue.

Another issue I have seen or experienced are air leaks at fittings on the tank, especially seals around access plates and gauge senders. This usually results in a rotten egg smell when flushing as air is being forced out of the tank into the bilge. The problem can be exacerbated by clogged charcoal vent filters. After a while the smells dissipates till the next flush. They can be hard to trace but putting some foaming soapy water around the fitting and then flushing will help as you can see bubbles where the air escapes.

First, be sure that its the black/grey water that's causing the problem. My odors come about because of my anchor chain locker. We gunk at lot. We wash the chain as it comes in. The chain goes into a locker. Unfortunately the locker does not drain overboard but directly into the bilge - that brings all the left over mud etc right into my bilge. If I don't regularly clean that forward part of the bilge, the front stateroom is usable

Beau brings up a good point. Your grey/black water odor is a bit broad. You could suffer from an odor problem from a number of things.
AND, as before noted, hoses are usually the black water culprit. Rode lockers, overflowing shower & A/C sumps can contribute quickly.
Not familiar with your rules where you're at, Do you collect grey water or sump & pump? Any condensation observed it he bilges or liners?
Are you ever able to clear the odors for any time?

I remember a boat that I invited my wife's girlfriends on to utilize their noses. Every weekend they would come onboard and help me trace down an odor after replacing hoses, vinegar sprays in the E R and rinsing all the sinks, showers and sumps. 4-5 weeks later, found an overflowing A/C tray dripping into a non-draining bilge pocket way forward. No more stink, no more wine for da girls.
Sorry I found it or they'd still be coming over.....

Please tell us us what idiotic builder drained the anchor locker in the bilge! There is no excuse for such pathetic design

Post Yachts?

Bertram, Hatteras, Stryker, SeaRay, Bayliner (US Yachts), Bayliner Trophy, Huckins, Most wanna-be big boat builders, I have witnessed.

would you consider draining the anchor locker to a clamshell on the outside?

I'm sure a lot of owners would like to drain to the outside. If the locker base was way above the water line.

How about NO anchor locker drainage !!!

I usually don't experience smell from gray water too much, but clean the sumps if they're exposed. Black water is the usual source of foul odors. I would definately use raritan treatment, the blue stuff, it makes a huge difference.
What I would check.
1. check vent and make sure it is free and clear.
2. If vent filter hasn't been changed in 2 years or tank has been overfilled change,
3. Check top of tank for any fittings that could be leaking
4. Check hoses and if they're old or in poor condition change them.

Agree with everything said about changing hoses and the filter if you have one. If you have standing water in the bilge, a little hydrogen peroxide regularly will keep it relatively odor free inexpensively.

Thx RT that would be the smart thing to do, but after 16 years, its almost a rote chore.

Never thought about it, but I make it one of my 'to do' projects...

I think we posted a thread in our owners forum that ended up identifying about 28-30 different potential sources of odor. Often little things here and there (standing gray water in sink P-traps, for example) and the solution to each of those can be slightly tailored (e.g., flush the P-traps). Rope locker drainage was one, stagnant AC condensate, shower sump, bilge water, batteries off-gassing, and so forth...

-Chris

White vinegar is another stink buster

there might be 100 sources of annoying odor on a boat.. 90% of the time it's the black water system..

FWIW, many of our members found that even though they had immediately attributed odors to black water systems, the real source more often turned out to be something else.

-Chris

No I agree that 90% of the time bad odor comes from the head/holding tank system.