Cheapskate waste tank vent filter

Oct 24, 2010
2,405
Hunter 30 Everett, WA
I'm posting this here knowing it may belong in the holding tank area. I put it here because I felt more folks might see it.

We have been plagued with waste tank odor. This is usually due to me not putting chemicals in often enough. Here is a fix. Install a waste tank vent filter. The problem is they are expensive (around $120) and need replaced annually. Here is a cheapskate fix for a do it yourselfer.

Parts list:
10 inches of 1 ½ inch PVC pipe
2 each ¾ inch slice of 1 ½ inch PVC pipe
2 each ½ hose barb adapter (or what ever your vent tube size is)
2 PVC 1 ½ inch end caps
Open cell foam (the more porous the better)
PVC cement (I used clear)

Directions: (this took me less than 30 minutes)

Cut PVC pieces to length.

Slice through with a hacksaw then heat and bend the ¾ inch slices of PVC to form mounting brackets to clamp over the 10 inch tube. Drill mounting holes in the brackets.

Drill the end caps to accommodate the hose barb and glue them in place. I used clear PVC cement knowing the cement may not do much on the nylon adapters. 3M 5200 might be a good selection for this, but I drilled the hole a bit small so it is a really tight friction fit. Once P put some glue on what will be the contact area of the fitting I pressed it in place with light blows from a hammer.

Glue only the lower end cap in place
Cut foam in a wedge shape and push it into the bottom of the pipe. The wedge shape is to allow a greater area of the foam to allow less restriction in air flow.

Fill the pipe with activated charcoal within an inch or so of the top of the pipe.
Place foam over the top of the charcoal
Place the second end cap on the tube (a firm friction fit is good.)

Mount it in series with your waste tank vent.
Annually (or more often if needed) remove the filter, clean out the charcoal and replace it. I purchased activated charcoal from a pet store intended for fish tank use. The container should refill the filter for a number of years.

I already had a short piece of 1 ½ inch PVC pipe so the total cost for me was less than $25 including having purchased the wrong size fittings the first time and the milk carton size package of charcoal.

I hope this helps
Ken
 

Attachments

Apr 8, 2010
1,606
Frers 33 41426 Westport, CT
Nice work, but, and someone correct me if I'm wrong, I believe that generally at least 3/4" if not 1" is the suggested vent hose size, with 2 vents from opposite sides of the boat recommended so it creates cross ventilation.

With enough cross ventilation you shouldn't have any odor to filter out.
 
Mar 26, 2011
3,962
Corsair F-24 MK I Deale, MD
That should work for you. A few tips:

1. 2" x 12" is the standard design for these filters.
2. The carbon generally lasts 2-5 years. You have a smaller pipe but should get 1 year easily.
3. Better be careful with install--if the carbon gets wet or is high enough it will plug and the tank may blow or implode. Mine is rigged with a by-pass, easily done. At the very least, mount it HIGH and don't let the tank get full!!!
4. 5/8" is the most common vent size (code). But you see some of everything.
5. If I couldn't thread I would use a conduit nut (they come in pipe sizes) on the inside instead of just glue.
6. Make certain the hose is sanitary; other wise the hose will permeate and you will smell that. Or it will kink.

Cross venting as an alternative? I did a bunch of testing on that and it works fine, assuming the hose are short and the locations workable. Another solution with its own limitations (more hose, another tank fitting and another through-hull, chemicals are needed, somewhat less effective). Much depends on the boat. The simplest solution is a BIG single hose with a very short run, but even then the fitting better not be upwind of a window.
 
Jan 6, 2010
1,520
Ken,

I have found with my system, if you were getting bad odor from your waste tank gas, there are three ways this may be happening. There was not enough detail in your post on what you had troubleshot prior to the filter, so here are my thoughts.

1. Where is your vent hose & where does vent to the outside? If you have this, make sure the hose is not leaching odor. Also check that the vent fitting is not clogged or hose crimped.

2. I assume you have a standard type marine head w/pump. If the pump seals are wearing out odor will happen.

3. Sanitation hoses can also leach odor if they are old.

I've had over the years, all of the above problems. There's nothing worst than opening your boat to a foul odor.

CR
 
Mar 26, 2011
3,962
Corsair F-24 MK I Deale, MD
Ken,

I have found with my system, if you were getting bad odor from your waste tank gas, there are three ways this may be happening. There was not enough detail in your post on what you had troubleshot prior to the filter, so here are my thoughts.

1. Where is your vent hose & where does vent to the outside? If you have this, make sure the hose is not leaching odor. Also check that the vent fitting is not clogged or hose crimped.

2. I assume you have a standard type marine head w/pump. If the pump seals are wearing out odor will happen.

3. Sanitation hoses can also leach odor if they are old.

I've had over the years, all of the above problems. There's nothing worst than opening your boat to a foul odor.

CR
There is a fourth cause, which lead me to vent filters. The vent fitting is EXACTLY upwind of one of the main roof hatches (catamaran). From flush to stink, if on the hook with a roof hatch open, is a matter of a few seconds. The stink is noticed by those in the salon, not in the head. Better ventilation and chemicals helped (I tested forced aeration with a pump just as an experiment and it helped) but a filter eliminates the smell 100% without cutting holes.

I also use a small amount of nitrate-based chemical as it helps with pump-outs and reduces the load on the filter. We keep it in a spray bottle (diluted) near the head and spray some in after use. It also helps with bowl related odors.

If increased ventilation combined with a good treatment chemical (Oderlos, Camco Ultra, and anything based on nitrate) solves the problem without a filter due to different vent location, that's great.
 
Oct 24, 2010
2,405
Hunter 30 Everett, WA
Thanks everyone.

It is in fact a small hose to only 1 vent. Putting one on the other side of the boat would be problematic. Having said that it's also a small tank, so I would expect less natural venting when not flushing or pumping.

I do use quality tank chemicals. I can't remember the brand right now, but it's the one I've heard the most praise of across the web. The filter will be mounted high (just below the deck above the V birth) and I watch tank levels regularly. The odor is when we flush wherever down wind is. I did already replace the toilet and hoses. Toilet replacement wasn't due to odors, it was cheaper than the parts to fix the old one.
Ken