David,
I'm sorry to disagree but you need to understand how the biology of a holding tank is supposed to work. A good system doesn'r need Odorles, KO or a vent filter.
This article was taken from Peggie Hall's Library of Classics. I can't post the link as it would be a violation of this site's rules. Many here will vouch for Peggy's creditials. The article clears up some myths about holding tank order and how to NATURALLY eliminate it. Bottom Line, add more air to your holding tank by installing an additional ventilation line.
Getting Rid of Holding Tank Odors by Peggy Hall
Odor out the tank vent line and odor inside the boat are two separate issues. While it's entirely possible to have both, it's equally possible to have one without the other, and each must be dealt with separately. Odor out the tank vent line originates in the tank, not in the plumbing, while odor inside the boat can be due one or more of several causes--including the plumbing--but unless a tank is leaking, nothing you do to the tank contents will cure it. Here, we're only going talk about odor out the tank vent line.
What very few people in the marine industry have learned, and why there is so much folklore about odor, is the very nature of sewage-of ALL organic matter--and how it breaks down, what creates odor, and what prevents odor from forming. Once we understood these principles and learned how to apply them to onboard systems, we were able to install systems that are completely odor-free and correct the ones that weren't. Once you understand it-and it's so simple!--you can do the same thing.
There are two ways to deal with holding tank odor: try to reduce it, mask it, and contain it after it's formed, by using chemicals and filters-which has never proven very successful…or prevent odor from forming in the first place.
Sewage-all organic material--contains both aerobic (needs oxygen) and anaerobic bacteria (functions in an airless environment); But only the anaerobic bacteria produce foul-smelling gasses! Both aerobic and anaerobic bacteria break down organic matter, but when organic matter breaks down aerobically, it does not generate odor-it converts to CO2, which is an odorless gas. So, as long as there is a sufficient supply of air to the tank, and an aerobic bacteria treatment is added to aid that which naturally occurs in sewage, the aerobic bacteria thrive and overpower the anaerobic bacteria, and the system cannot produce odor.
A bio-active (Iive aerobic bacteria) holding tank treatment such as Raritan "K.O." works with the aerobic bacteria in sewage, eliminating odor, completely emulsifying solids paper, and preventing sludge from forming. Enzymes do little if anything-a brief respite from odor immediately after adding them, then odor begins to build again. Chemical products mask odor with another odor, and they kill not only odor-causing anaerobic bacteria, but beneficial aerobic bacteria as well-not good, because the aerobic bacteria are needed in the system to break down and emulsify solids and paper. Otherwise, they only break UP and dissolve them into little tiny particles that settle to the bottom of the tank, along with chemical residue, to become sludge that turns to concrete. Plus, chemicals, unlike bio-active products, are also unwelcome in landside sewage treatment facilities, and are especially unappreciated by those living and working near them!
Anaerobic bacteria produce a variety of sulfur monoxides and dioxides (which are the malodorous gasses), methane-which has no odor but is flammable-and carbon dioxide, which also has no odor but can create an anaerobic environment if there is insufficient ventilation to dissipate it. Carbon dioxide does not rise or fall, it is ambient-like the atmosphere, but heavier than air. Without a sufficient flow of fresh air through the tank to allow it to dissipate, it simply lies like a blanket on top of any pool of sewage (whether inside hose or a holding tank) and builds, creating the perfect environment for the anaerobic bacteria to take over. The system literally "turns septic," and the result: foul gasses out the vent line every time the head is flushed.
So in the holding tank, the key to odor control is the vent line; it must allow a free exchange of fresh air for the carbon dioxide generated by the sewage. Therefore, those bladder tanks which have no vent are all but guaranteed to stink; there's no source of air into them at all. Boat builders, boat owners and boat yard personnel who install holding tanks have always viewed the vent line only as a source of enough air to allow the tank to be pumped out without collapsing and as an exhaust for methane (Many even believe methane-which in fact is odorless-to be the source of odor.) Some take the attitude that tanks must inevitably stink, so the thing to do is run that vent line as far from people areas-cockpits, sun decks, etc.-as possible, or make the line as small as possible, or install a filter in it. All of the above actually create the very problem you want to solve.
Think of the holding tank as a stuffy room which needs to be aired. You know that even if there isn't a hint of a breeze outside, just opening a window will allow the fresh air outside to exchange with stuffy air in the room. Open another window for cross-ventilation, and the air exchanges even faster. However, just opening a skylight accomplishes nothing unless there's also a mechanical means (an "attic fan") of pulling the air up and out-and that won't work unless another window is open to create airflow. But the only "window" into a holding tank is at the end of a "hallway"-the vent line. If that "hallway" is too narrow and goes around corners, takes a long and curved path, or rises more than 45 degrees above horizontal, no ambient air can find its way to the tank to dissipate and exchange itself with the gasses in it.
The tank vent line should be as short, as straight, and as horizontal as possible, with no sags, no arches, and no bends. The minimum I.D of the hose (which is the "standard" size in use today, but for no reason other than being "standard" in fresh water and fuel tanks) is 5/8"; we recommend that it be at least "", and prefer 1" or even larger. Ideally, it should be no more than 3' long. If it has to be longer, or if running the vent line uphill more than 45 degrees off horizontal can't be avoided, or if it's impossible to run a vent line that does not go around a corner, increase the size of the vent line to 1" or even larger. If, for instance on a sailboat, the line must go up to the deck, install a second vent line in order to create cross ventilation, or install some mechanical means of forcing air through the tank. Because powerboats don't heel, a tank can be located anywhere in the boat that's close enough to the hull to allow the vent line to be short, straight and relatively horizontal. On sailboats, or any time the head is forward, we prefer to put holding tanks in the bow-under the v-berth-because the hull just behind the point of the bow is the only place on the hull except the transom (which is not a good location for a single vent line) that will never be under water even when the boat is at maximum heel. It's the perfect place to install vent-line through-hulls, because the though-hull is always into the wind, forcing air into the vent line, when the boat is underway or on an anchor or mooring. The vent through-hull should not be the same type as a fuel vent through-hull (a cap with a slit in it), but should be a be a straight open bulkhead type through-hull. On sailboats especially it's advisable to vent off the top of the tank and not the side, because heeling can cause the contents of a half-full or more tank to run into the vent line.
Because a filter blocks the flow of air into the tank, install a vent line filter only as a last resort; the filter does trap the gasses which try to escape through the vent line, but a filter will not stop gasses from forming, and therefore from going back up the inlet hose into the boat or up the outlet hose-and eventually permeating even the best hose.
Check the vent line regularly for blockages; little insects love to build nests in them. And remember-the vent line is not an "overflow!" So try never to overfill the tank-and if you do, backflush the vent line thoroughly with water to remove any bits of sewage can clog it. It's possible for enough air to pass through it to allow the tank to be pumped and gasses to escape, but that doesn't mean the line is completely clear of any blockage.
Finally, the system, including the tank, should be at least nominally rinsed, through the head or back down the deck fill-with fresh or salt water-after each pump-out, and occasionally with fresh water. If your marina doesn't have a dock water hose for this purpose, please ask them to install one. It should be separate from the potable water hose, both should be clearly identified, and the two should never be used interchangeably.
.