holding tank smell

Lesser known, there was a 1 1/2" model separate from the 5/8" model.
Now it looks like the old 1 1/2" model is not available any more but a new uni model.
I'll check it out when it comes in.

It's been suggested but worth repeating. Check your shower/gray water sumps. I recently installed 2 new vacuflush toilets. About a week later, I noticed a very strong sewer smell from the master stateroom. I checked all of the hoses and clamps on the new head system thinking that had to be the source. They were all tight with no leaks on new lines. When I pulled the inspection cover to access the shower sump, wholly crap, the smell almost brought up my lunch. It had been about 60 days since I had cleaned the sump. The build up of soap scum and all that grows on it was the problem.

Someone mentioned regularly pouring some Mr. Clean down the shower drain to help keep things clean. I'll certainly give that a try.

Peggy Hall, the "Potty Princess", recommends Raritan CP for shower sumps. We've used Noflex for some time and are happy with it for the black water tank.

I'm an RVer and have experience with tank odors. Most come from the grey tank, as others have stated. I found a product that really works. TankTechs, it can be found on Amazon with listings under both RV and Marine....same product just different labeling. Been using it for little over a year now and it stopped the odor, cleaned the scale off of the tanks and even cleaned up the sensors so that they work again.

No affiliation with the company, just love the product.

A simple way to reduce odor and FOG buildup in gray water tanks is to use Dove soap. Dove will also reduce the residue on shower walls due to the softners in the formula.

Highly scented bath soaps like Dial and Irish Spring create a significant sticky fat buildup in shower sumps.

There are also new chemical formulations in vent odor filters that make them substantially more effective at odor reduction over typical bituminous carbon for those cases where the odor source is the vent exhaust point.

Yes I use Noflex as well in my black and gray water tanks. Very good product although expensive.

Another vote for Noflex digester.
Another vote for fresh water flush.

#noseawaterinmyboatplease

I thought she was the "Head Mistress" and I don't mean boarding school

You maybe correct. Sounds much better.

Peggie has a great book on marine sanitation it is worth the read.
I'm happy everyone likes the Noflex.
It maybe expensive but a little goes along way .
Where the expense comes from is the freight and all the people in the middle taking a piece of the pie
But they are the people that support the product 100%
There will be a new version coming out for home septic next spring if you have septic problems it works great

This.. and I think you're the first one to mention it that I saw in this thread. Very often oldor complaints around the holding tank and its affiliated plumbing are in fact cuased by stagnant sea water on the INTAKE side with critters decomposing in it. Next thing you do is flush it into your "diffuser bowl" and into your black side plumbing. One solution is fresh water flushing, but that requires a good supply of fresh water. There are other solutions which require even more creative plumbing.

As far as the RV comments.... I've been working with grey and black water for many years. A PROPERLY designed, vented and otherwise sealed system needs NOTHING added to it. I never use any kind of chemical/additive and I have zero odors. But, in RV's things go downhill below the floor into a somewhat vented area and stay there until they go downhill outside. Not the same as a boat where it's all inside the closed vessel.

When we have the pump out dock and nobody waiting behind us, we will flush the heads and tanks several times.
The showers have hand held showers heads and can reach the heads increasing the amount of warm water to the tanks and better rinsing.
At some docks, were taking on fuel at the same time and continue rinsing and pumping out till our fueling is near complete.
No odors in our bilges sense the tank and hose upgrade a few+ years ago.

In the RV world the better installations have spray nozzles installed in the tank with a garden hose connection at the dump handle location. Thinking about this I've never seen these on boats. I think that would be something to consider. Easy to install in a polyethylene tank. There's cheap kits out there.

Oh, I like this idea.
I have Todd tanks. A few extra fittings are caped off. I wonder to install some internal tank sprayer to help with the rinsings.

Here Capt Ralph. May have to lengthen hose etc but for the money it's a good start.

https://www.amazon.com/Camco-40126-...ith+Back+Flow+Preventer&qid=1576157636&sr=8-2

We have an internal tank sprayer in our 50 gallon holding tank. Along with a big orange charcoal filter on the vent side. No problems with odour and the sprayer at each pumpout does a great job.

In my RV I also use the Geo method. You simply dissolve 2 cups of water softener in warm water, add 1 cup laundry detergent and pour it into the empty tank. The water softener makes all the interior surfaces of the tank, sensors, etc slick so nothing sticks to them. When you dump the tank everything comes out nice and clean and odor free. I haven't experienced a need to do this in the boat but wondering why it wouldn't work the same as the RV?