Holding Tank treatment for odors

Delta, if you describe how you use the MSD system we might be able to give you better advice rather than "listing our favorites".

In the area of add-in treatments, there are a few basic types:

Fomrmaldehyde based disinfectant. Usually blue. This combination kills -everything- in the tank, and often includes perfumes to make the resultant residue more "nose friendly". Your neighborhood ecologists will hate you, however.

Oxidisers, including bubblers. This group of products change the tank environment to an oxygen rich environment vs anaerobic. Since it is the anaerobic bacteria that cause the most offensive ( and troublesome ) byproducts, encouraging the aerobic bacteria reduces/removes the odors. The result is normally environmentally tolerable. This is especially desirable for those who can pump their holding tank overboard ( outside the three mile limit ). If you always pump out at the dock, the only benefit is the fact that you are not pouring toxic waste into the sewer system. Some of these systems ( bubbler, "K. O. ) add/promote active aerobic colonies and in the long run are cheap, because you do not need frequent replenishment. Pure chemical additives ( ie: Odorlos ) add nitrates and such to produce the oxygen rich environment and require replenishment. These are easy to use but are more expensive in the long run.

There are other systems, as well...

-edit-
There is no one ideal "one size fits all" system. Perhaps if you gave us a bit more info on usage, location, pumpout availability, we could make a few useful suggestions..
 
Here are some specifics:

The holding tank is a 42 gallon white plastic tpye tank with a vac-u-flush head. We pump out at the dock almost after every overnight weekend outing. Some times it might be every other outing. I had been using KO up to now. The last time we used the head to flush waste down was in December. We than pumped put the tank and added KO. We have not used the head to flush waste down since than. This is fairly tipical for us during the winters here.
About a month ago we developed some smelly odors in the bilge were the tank is located. This is the first time over 5 years that we have had any odors. The vent is clear and the filter was changed about 6 months ago. We have checked the hoses and find no leak. I'm now wondering if I should switch to some other treatment brand. Thanks for any help!
 
a) The key to KO is fresh air availability. Normally the last thing you would want would be a filter in the vent line, as that slows the exchange of ( needed ) air. In fact I have heard of some people adding a second vent to promote the air exchange. If it were me, I would remove the filter, and keep on using KO, adding a second vent if needed. When KO works, it really works well.

b) While I'm no tree-hugger, it still bothers me to use the formaldehyde based stuff, so I would suggest Odorlos as a second choice. This would add oxygen to the solution and allow the aerobic bacteria to "do their thing".

c) Throw your hands up and use the blue stuff. You will need the vent filter if you do this, and in the event you switch back to Odorlos or KO you will need to throughly flush all of the chemicals out of the system or neither will work.

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I suspect that the new filter, for some reason, restricts air exchange more than the one it replaced. The result was that the HT went "sour". It could also be that removing the filter would remedy the problem.

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Another related, but different source of odors ( and the one I suspect ) is that the hoses in your system have permeated, and that is the source of the problem. The cure is to replace the hoses, as changing tank chemistry will not cure this problem. It the hoses are 5 years old, permeation is a very real probability. To test ( as I remember it, others please correct me on this procedure ) take a cloth rag, wet it in warm water, wring partially dry, leaving it damp, wipe the cloth over the hose, then see if the cloth contains the odor. It so, the hose needs replacing. ( possible error... you may need to drape cloth over hose for a while then remove. I forgot the details! )
 
I've used Calgon in the RV and the boat with great success. Don't know the eco-consequences though if you discharge into the pond. I usually put a cup in the bowl and flush it into the hoses and let it set there for a while until flushing into the tank.
 
Thanks Radioactive for the information. Decided to replace the tank and aLL hoses. You were right, the tank went sour and the hoses had bad smells. Not an easy job, but added bleach to the tank, washed it out with water and pumped out. Did this three times. Also did the same with the hoses. Had to clean the bilge out with diluted bleach because the tank never is completely empty after pumpout and when removing the tank there is no way to get it out without some stuff coming out. Wet vac'd out the dirty water and now the bilge is cleaner than when I bought the boat.
 
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