How sweet it is!

[Captain Gadget]

Well after many an embarrassing smell from my holding tank vent when the toilet was flushed knocking people over on my dock I installed a carbon filter and now NO SMELL!
A fellow boater mentioned that he made a homemade carbon filter using aquarium charcoal and pvc piping I decided that maybe I would do the same. Then I came across a old water filter that used 10 inch cartridges, so I thought why not?
I bought a granular carbon 10 inch filter put ¾ inch pipe connectors to fit in the filter. I then disconnected the holding tank vent (3/4”) hose where it goes to the through hull fitting. I connected it to the input of the filter container. I added 2 ft of ¾ inch hose from the output of the filter container to the through hull fitting. It is done. There is lots of height that no heel will ever allow fluid into the filter.
I tested it before installation (wow what a smell) and then after and (no smell) nothing, absolutely nothing. In fact I thought that maybe it was plugged so I sucked air out of the end of the clean new hose and there was lots of air moving and you know....even the air tasted sweet.


Just thought I would pass this on.

 

[David in Sandusky]

Oxygen is the answer!

As I understand it, the primary reason for the air tube in your holding tank is to supply oxygen to the contents. That's because the bacteria that use oxygen do not create an odor. The "anaerobic" bacteria that work in oxygen starved environments are the ones that create the smell. The secondary reason for the air line is to relieve pressure when the toilet is flushed, or the tank is pumped out.

As with most boats, our air line in inadequate, so we add oxygen to our porta-potty tank in the form of Odorlos, a powder or liquid. Staying on top of this approach results in _no_ odor from the tank. We are sure of this, since we open the tank to the cabin in order to use it. No foolin' this really works!

Your carbon filter solves the problem of odor when you flush, but it reduces the amount of oxygen that will enter through the pipe. As I said above, though, our experience is that an oxygen additive like Odorlos is the real answer anyway.

 

[MsEmee]

Pictures would be nice. Hard to tell how you did it with us novices.

 

[Mulf]

PEGGY???? My recollection of what Pegggy says....

is that the vent hose should run uphill as straight as possible. If you added two feet plus the length of the filter you probably do not have that. Hopefully she will see this thread and help straighten us all out (pun intended).

 

[Peggie Hall HeadMistress]

I just wish I could have invented something that...

...helps to create the very problem it's sold to solve...'cuz that's exactly what a vent line filter does. They do trap smelly gasses, but they also help to create those gasses by impeding the flow of air needed to keep the tank aerobic, which is essential to PREVENTING odor. Air/gasses can be pushed or pulled through a filter, but the filter doesn't allow it to flow freely.

They only last a year at most, are toast immediately if they get wet, which makes 'em an even worse idea on sailboats than on powerboats because location of vent fittings on most tanks allows waste to spill into the vent line when the boat heels. You claim that it's high enough to keep waste from getting into it...but that won't keep waste out of the vent fitting on the tank and/or that end of the vent line. Nor can a filter keep dust, pollen, insects, etc out of the vent thru-hull...and a filter in the vent line makes it impossible to backflush the vent line to keep it open. So your solution to one problem has actually created a much bigger problem: no way to maintain the tank vent without physically cleaning out the thru-hull and the other end of the vent line manually. And you won't know it needs it till you start experiencing the problems that are the result of a pressurized tank.

But...it's your boat...and nothing I say is gonna convince you to get rid of the bloomin' filter and do a few simple things that will actually eliminate the need for it by preventing odor in the first place. Best I can hope to accomplish is to convince others that installing a filter is a bad idea.

Mulf, you ALMOST got it right. The vent line should be as straight as possible, but it should be as horizontal as possible.

 

[Captain Gadget]

Thank you for your comments. Actually, the old vent line had a big loop that went up above the through hull fitting and then back down to the through hull fitting to complete its passage. The new filter does not really change this loop, just the filter at the top of the loop. Air flows both ways through the filter and there should be no increase in resistance to this unless it gets wet. I agree. I plan to change it every 2 months or so whether it needs it or not.
I know, Peggie says get rid of it and I guess go back to the smell. My buddy has had his for 3 years and no problem. Maybe I am wrong. But I am going to try it. I do not think it will impede oxygen into the tank much more than with out the filter.
Hunter installed my vent with a loop so the loop is still there. Really, it is just carbon soaking up the smell, air still moves back and forth. Hmmmm....
I will get a photo and post it. Very simple. If it does not work, it is simple to pull out.l

 

[David in Sandusky]

Give Odorlos a try in your tank. Seriously. it can reduce/eliminate the odor in the tank.

 

[Peggie Hall HeadMistress]

The loop in the vent line is a big part of the problem

Holding tank vent lines should be straight as an arrow...just straightening it out and using Odorlos would reduce your odor by at LEAST 75%...increasing the diameter to 1" (easier to do than installing the filter and wouldn't have to be changed every couple of months). would eliminate it.

The filter WILL trap odors out the vent. But it will actually increase odor in the tank...odors that will migrate into the hoses, permeating 'em, and back to the toilet to escape through the joker valve unless you also replace it every 2-3 months. So I'm sure your buddy is very happy about no odor out the vent line...and prob'ly believes that the odor inside his boat is "normal" unless they're really BAD...in which case, his solution is likely to be an ozone generator, which is even worse than vent filters 'cuz ozone is corrosive and damaging to rubber and hoses.

 

[LuzSD]

Backflushing the vent line..

........and a filter in the vent line makes it impossible to backflush the vent line to keep it open.






Peggy, can you tell me exactly how to backflush the vent line.....sorry, just not getting that one! Thank you!

 

[Peggie Hall HeadMistress]

Stick a hose nozzle up against the vent thru-hull and turn on the water! :dance:

However, because "vent " thru-hulls are all only 5/8" and actually designed to use on fuel tanks, many of 'em have screens or tiny pinholes...or worse yet, if your boat is a Catalina there is no vent thru-hull, just a slit in a rail stanchion (in which case, scraping out the slit with a screwdriver blade is about the only way to keep it from becoming blocked)--that's not as easy as it sounds. Those types of vent thru-hull are also the MAJOR cause of holding tank odor, 'cuz they allow NO air exchange through the vent.

The solution: replace the thru-hull--or on a Catalina, install a thru-hull--with the type in the attached photo. And as long as you're doing that much, increase the size of the vent to 1".

NOW all you have to do is stick a nozzle up against the thru-hull and turn on the water. Do it every time you pump out and/or wash the boat and you'll never have to deal with the consequences of a blocked vent.

 

[Captain Gadget]

Some have asked for a photo: here it is. Air seems to vent back and forth with no problem.

 

[Ron McCoy]

Why put up with "head odors" originating from the holding tank. My solution - pump out regularly and while I'm at it, I rinse the tank with fresh water and pump it out too. Do two or three rinses per pump out and you'll never have smells nor will you have to use additives. Real simple solution. Why keep cr*p on your boat that you don't need?

 

[dparilla]

Without positive pressure, air will not flow across a filter media. In this case, you tank only exchanges air when the pressure differential between atmospheric and the tank changes, typically a diurnal cycle, daily heat and cool, that is accelerated with either a flush or a pump out. The odor is essentially scrubbed from the air by the filter media, however it is very easy for this filter to be overwhelmed by odor. In essence, you are treating the symptom, not the problem.

 

[Rick D]

Vent Back Flush Five Dollar Fitting

This is my solution for back flushing the holding tank vent.

 

[Peggie Hall HeadMistress]

What does your thru-hull look like, Rick? Can you email me some photos that show what you've done in enough detail to let someone else build one? And the thru-hull fitting.