Holding Tank Vent Filter

[Viking76]

Last season, had a holding tank vent filter installed to minimize terrible odors escaping when flushing the head. Pumping out the holding tank now seems to have a problem of emptying very slow. When taking the pump out hose nozzle off the tank emptying fitting there is a woosh of air going into the tank emptying fitting. Could the vent filter be restricting air flow into the tank? Could the tank collapse or implode? Should the vent filter be eliminated?
Thoughts & Comments?

 

[Shadowcruzr]

Sounds like you are drawing a vacuum on the tank. I personnally dont like those filters. If they get too much moisture, they're hosed. I have a porta potti that I put chemicals in and I dont get any smells. The other thing to do is vent more air into the tank. This will help with the odors.

 

[PascalG]

yes, the woosh is a sign... you could collapse the tank or face a brown geyser if you open the pump out fitting after someone flushed !

the filter shoudl last more than a year... either it was installed in a way that let rain water of splash get to the filter or the tank overflowed once and clogged the filter.

 

[marich]

Something may have built a nest in the vent outlet and plugged it up. You should check that as well.

 

[HOGAN]

Yes, yes and yes

 

[nph]

You can disconnect the filter, and that will solve your problem, but why not just rebuild the filter. Most of the filters are made out of PVC pipe. 1.5" pipe to be exact and are filled with nothing more then activated carbon, and mesh that you can buy at the local pet store, It is used in aquarium filters.

Go to your local hardware store, get 2 PVC fittings and glue, 1-1.5" pipe to male thread fitting and 1-1.5" pipe to female thread. These to fittings with screw together and leave you with a "coupling fitting" that can be taken apart. That is so next year, you can just unscrew them to rejuviante your filter. Cut the existing filter in half, and dispose of the carbon that is in there, it will most likely be and packed to gether. You may need to replace the mesh sponge at both ends of the filter also, (can be bought at pet store with carbon)
I bought the mesh sponge and replaced both ends. I also cut a third piece that I used to help put toghter the filter.

1. Cut filter in half
2. Clean out old carbon and filters
3. Glue one fitting one each half of old filter
4. Place Mesh Sponge in both halves of fliter
5. Fill both halves with carbon
6. Place mesh sponge in end of one half to hold carbon in when you screw halves together
7. Screw two halves of filter together.

This cost me about $15 and I have enough carbon to do it 2 more times.

 

[bcatlin]

Speaking with a voice of experience...yes, your tank can and will implode. Not a pretty picture taking it out of the bilge area!

bcat

 

[pdecat]

Spraying a hose into the vent outlet kills many filters.

 

[bazza]

I have seen many threads on this forum on this. The filters are toast if they get wet.End of story. Here in the charter industry in the BVI there are many cats and from stock they all have the same problem. We do not have any pumpout facilitys here and everyone has to dump while underway and out from shore. That causes a problem as the vent line exits the hull fairly close to the water and when dumping while underway, air must re-enter the tank via the ventline, with the vent down low and sailing in only average seas the filter can be toast on its first day out. The answer that we have come up with is to install a "T" in the line between the tank and the filter. The teed off hose goes to a non return valve to allow air to enter the tank but not to exit. Next a tee is put in the line after the filter and before the outlet vent. the non return valve is also connected to this t. Lastly another non return valve is placed between the second t and the filter so air can go out of the filter thru the nrv and out the vent. so now when we flush, vent air still must go thru the filter,thru the second nrv and out the vent. When dumping air comes in the vent,thru the first nrv and into the tank. Net result is the filter cant get wet unless you overfill your tank and there is no filter in the incoming air to restrict when dumping and any moisture in the vent misses the filter.
Bazza.