Poor venting by design

Aug 15, 2019
4
Niagara 35 Berkeley
I just replaced the holding tank, Y valve, and all hoses and clamps, and fully serviced the Raritan PHII on my new-to-me Niagara 35 "Classic".
But it still stinks! In fact, it has the same stink, although not as bad, as it had before I replaced the 20-yr-old hoses and did 2 rounds of NosGuard.
My nose has traced the odor to the tank, a new 24 gallon Todd "heavy duty", but there doesn't seem to be any specific source, i.e. no leaks from the fittings or loose hose clamps. Since it doesn't get noticeably stinky until the tank gets about 60-70% full, I suspect it's at that point that the ratio of sewage to air exceeds some threshold of de-stink-ability that no amount of my usual go-tos (Happy Campers or Odorlos) can handle.
I just bought CP and KO locally -- and the book, pending shipping -- so I'm going to try those after tomorrow's pump & flushes, and I'm going to use only freshwater in the toilet per a dock neighbor's recommendation.
In case those changes don't help, I just ordered NoFlex Digestor and will try that on the subsequent tank. Just learned of that product on this forum.

However, I suspect none of that will work. I suspect the real culprit is that, due to the unusual layout of this boat where the tank is right in the middle of the cabin, fresh air exchange is essentially nil. The 15' 3/4" vent hose has to go up 18", then back down 30" until parallel with the bottom of the tank (running next to the outlet hose), and finally back up 5' to the gunwale. This doesn't seem conducive to good exhaust or air intake, right? And fresh air is the name of the game, especially in salt water, right?
If the aforementioned chemical solutions don't work (or any other chemicals, I'll try anything!), and getting more fresh air is the only fix, I'll next consider:
1. Installing the Groco SweetTank system, if I can find it
2. Adding a 2nd vent line and putting a closed inline fan -- like a tiny bilge blower, if I can find such a thing -- in the hose to force air circulation.

ANY suggestions, comments, criticisms welcome! Full time liveaboard here...getting desperate.
 
Jan 11, 2014
4,061
Sabre 362 113 Fair Haven, NY
The 15' 3/4" vent hose has to go up 18", then back down 30" until parallel with the bottom of the tank (running next to the outlet hose), and finally back up 5' to the gunwale.
@Peggie Hall HeadMistress will no doubt have more ideas. The first thing that jumped out to me was the vent hose. Essentially the hose has a trap, like the one under any shore based sink. Any liquid that finds its way into the vent hose will settle at the bottom blocking air flow. When the head is pumped the pressure will blow air past the water block, however, it will not passively allow air to flow or it will restrict the flow.

A second and perhaps minor problem might be other things in the area smelling. Some things, plastics in particular, can pick up odors from other sources. On my boat when I started replacing some of the wiring I found the wires near the old smelly sanitation hoses had picked up the odor. Try liberally dousing everything nearby with PureArye (Pureayre.com).
 
Jan 1, 2006
4,110
Marblehead Skiff 14' Greenport, NY
I think it's fair to say for any holding tank situation more frequent pump outs is a good thing. You state that the odor begins at 60 to 70% capacity. It's not possible for everyone to pump out every Monday or whatever but I believe it would help if it's possible for you.
 
Jul 20, 2005
2,422
Whitby 55 Kemah, Tx
The vents on holding tanks aren't for the air in the tank to be constantly flushed out (keeping the tank air fresh), but to allow stuff to be pumped into the tank and the tank be drained. Without a vent to allow air to be pushed out or sucked in, those two would not happen.

If you add a second vent as some have, it will flush the air depending on the wind, but, it will also allow sea-water to get in much easier. Choose what is best for you.
 
Jul 27, 2011
3,309
Bavaria 38E Alamitos Bay
I think it's fair to say for any holding tank situation more frequent pump outs is a good thing. You state that the odor begins at 60 to 70% capacity. It's not possible for everyone to pump out every Monday or whatever but I believe it would help if it's possible for you.
Agree. The best general solution to head odors that I’ve found is to keep the tank empty (i.e., pumped out) as much as possible, regardless of its degree of fullness prior to emptying. Our boat very rarely lays in its slip more than a few hours at a time, at most one or two days, with any sewage in the tank. When the tank is pumped shoreside it receives 3 to 4 rinses with fresh water. If discharged at sea, 1 or 2 rinses with seawater. Also, when pumped out shoreside, much fresh air is sucked in via the vent and circulates the tank. Of course, if you’re anchored someplace where you cannot readily pump out or discharge, and the tank is allowed to fill up over a few days, say, b/f it can be emptied, then apply your chemical treatments until you can empty the tank, etc.

Also, consider that if takes several days to a week or more to get the tank to 70% from lack of routine emptying, that long incubation period alone might be the greatest contributor to the odor problem, etc., as you evidently suspect. I regard these chemical treatments only as interim “solutions” pending a full pump out or discharge of the tank, not as an approach or strategy to combat odor with sewage in a tank for relatively long periods.
 
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Aug 15, 2019
4
Niagara 35 Berkeley
Thanks for the speedy feedback, everyone; new forum user and happy to see this!
I agree, the best solution is frequent pumpout trips to keep it as empty as possible. That's the preferred approach, and the one I anticipate using most of the time. But there are periods, during repairs, extended bad weather, etc., where it may not be possible to pump out for a couple of weeks, and it's during those times that I'd like to count on the system to provide odor free service.
I guess my frustration is in comparison to experience on my prior 2 boats where I similarly replaced everything and used tank chemicals, but never had an odor problem. On those boats, I used pick-up tubes so there was never standing sewage in the inlet & outlet hoses, and the vent hoses were <3' and nearly straight up to the gunwale. They could sit 3/4 full for up to several weeks before any odor was noticeable. So I think it's possible for sewage to sit for long periods -- not that it's desirable, of course! -- without a problem if the system can be, and is, well set up.
The new Trident 101 inlet/outlet hoses on this boat all pass the rag test, so that's why I still point toward ventilation, and wonder if improving ventilation to the Niagara's peculiar setup via the Groco or another "active" system will really, actually make a difference and let me use more of the tank's capacity and go longer between pumpouts when necessary, or whether nothing will help and I really have to be vigilant about pumpouts every week or at about 50% full, whichever comes first.

Oh, and I'm going to try PureArye, first I've heard of that, too. I emptied the boat, washed down all surfaces, and did two overnight NosGuard treatments before I started the sanitation rebuild, so I don't think it's other boat components retaining odors. But I'll try anything new.

 
Jan 12, 2016
209
Hunter 410 Ladysmith, BC
I have found that Zaal Noflex Digestor works better than odorlos or any other product for eliminating odours from the holding tank/head hoses. I would definitely consider a second vent to the tank on the shortest run as possible. Way cheaper and less work than adding the sweet system by Groco.
 
Oct 22, 2014
9,983
CAL 35 Cruiser Portland OR, moored EVERETT WA
You might ask the marina where you keep the boat if they have a pump out service.

Up here is has become a thing at marinas. A boat pulls up beside your craft. Runs a hose to your pump out thru hull. Opens the cover, pumps the effluent, closes the cover and moves on. Once a week or when called. Free service up here. Part of the Keep the Sound Clean program. Our boat taxes at work.
 
Aug 15, 2019
4
Niagara 35 Berkeley
Yep, we have BayGreen and they do it 1x/month for liveaboards, which of course I take advantage of. Cost is not killer for additional services so I could have them do it more frequently and never leave the dock, but I do like to pump out myself so I can be sure it's flushed thoroughly and be alerted to anything that doesn't seem right (air leaks, clogs, etc). They make it easy to keep the "holding tanks don't work so just keep the tank empty as much as possible!" attitude, but I have to admit I like a challenge, and if there is a way to have a usable system, I'm not going to give up until I've exhausted all options. If I were never going to let sewage sit in the tank, I could have just use cheap hose and a bladder tank and put the $ saved toward a few years' worth of pumpout boat services instead!
A 2nd vent is under consideration, but frankly it's the routing that's an issue. All hoses from the tank have to go up and down and up and will be at least 12', so I don't think it will improve anything without incorporating a fan to force the air to move.
 
Feb 26, 2004
20,692
Catalina 34 224 Maple Bay, BC, Canada
A 2nd vent is under consideration, but frankly it's the routing that's an issue. All hoses from the tank have to go up and down and up and will be at least 12', so I don't think it will improve anything without incorporating a fan to force the air to move.
Welcome. You posted in the right forum.
Pretty soon Peggie should be able to chime in.
Your issue IS the venting.
Peggie usually suggests email or phone calls, yup, real live and in-person. She's a gem! She'll help you with routing, too.
Good luck.
 
Dec 2, 1997
7,363
- - LIttle Rock
How many times will I have to tell y'all that unless a holding tank is leaking, it's rarely if ever the source of odor INSIDE the boat...'cuz odor from inside the tank has only one place to go: out the tank vent.
You said you replaced very stinky hoses...so I suspect your odor is residual odor from those hoses that has attached itself to all the surfaces in the areas they passed through. Todd tanks are pretty thin-walled, but not so thin that odor can escape through the tank walls.
So thoroughly clean all the surfaces, nooks and crannies the stinky hoses passed through, INCLUDING the outside of the tank. Use detergent and water, nothing else. When it's all at least 90% dry, spray a fine mist of PureAyre PureAyre (available from pet supply stores and Amazon) on every surface, nook and cranny. A pump garden sprayer is the easiest way to do that. DO NOT Rinse...just let it dry with all hatches open for 24 hours. If you still have a trace of odor in the boat, you missed a spot or there's another source unrelated to your sanitation system. A bilge in need of real cleaning instead of just dumping some product into it and letting it slosh around, then letting the bilge pump drain it, can make a whole boat smell like a swamp or even a sewer.

--Peggie
 
Aug 15, 2019
4
Niagara 35 Berkeley
Thank you, Peggie! Just last night I was reading that advice in your book. Going to pick up the PureAyre after work today.
But here's an update: I went to pump out and do extra rinse cycles at the pumpout dock Saturday in hopes of starting a CP/KO regimen. While filling with water, I scrubbed the vent screen with a wire brush and doused it with soap to bubble-test it as continued water input led to air displacement. But instead, a quick burst of liquid released from the vent and then nothing more...no bubbles. Hmmm. Next I pumped out the water that was in there to try again, hoping maybe scrubbing the screen freed up some gunk that the suction will clear out.
I went below as the fresh water was filling it the second time. (I'm usually singlehanded so I admit I haven't gone below during pumouts before). I saw what you see in the photo. Bubbles courtesy of Dr. Bronner's, which was the closest thing I had to a detergent aboard at the time -- of course, Dr. B's is just vegetable oil, which I now know is exactly the wrong thing to use, thanks to the book. Hard to tell from the photo, but the tank was inflated more than I thought a "heavy duty" tank should be. That inspection port cover was as hand-tight as I could make it at the time of installation. Starting to regret that I was too impatient to wait on a custom tank when I did this project.

So my conclusions thus far:
1. Vent is blocked and gas is escaping through the inspection port.
2. Inspection port does not seal well, at least certainly not when the un-vented tank is distorted due to lack of venting.
3. Blockage could be at the tank end or in the hose, likely in the unavoidable (by design) hose sag due to overfilling or sailing with too much sewage in the tank in a sloppy sea state (common conditions here). I opened the inspection port (slowly!) to relieve pressure and, expecting to see fully liquified contents, saw a layer of nearly solid stuff, some of which may have found its way into the vent hose at some point and stayed there. I sprayed the hose inside the tank to break up some of this layer, but some remained after several rinse cycles, presumably since the outlet is at least 1/2" above the bottom of the tank. Not sure what to do about that...I intend to continue checking the tank contents as I vary tank management schemes to see what actually works for liquefaction. Odorlos was used in this last tank full, albeit without proper venting so I won't dismiss it yet.
4. Inlet, outlet, vent, and unused vent ports on the tank are well-sealed. I saw no leakage from those despite the tank appearing ready to explode. At least one positive came out of this.

My current remediation plan:
1. Replace the 5/8" vent fitting with a mushroom thru hull, then use it to blast the hose with water, pour in white vinegar, etc. to clear out the blockage. Remove the hose from the boat and do it the messy way if I have to. Just get the vent cleared and working again.
2. Fabricate a wrench to close the inspection port with enough torque to ensure the gasket is really squeezed down. Add more thread tape.
3. Do Peggie's PureAyre method until boat is odor-free again so I know I'm starting with a clean baseline to detect any failure in the fix.
4. Improve ventilation. I'm debating replacing the existing 5/8" line with 1", or adding a second line, possibly on the port side (will have a sag just like the current starboard hose, though). There is also a possibility of routing it nearly straight up through the coachroof to some sort of vent fitting or the existing Dorade box. But exhausting right in front of the companionway doesn't sound pleasant. I could put a charcoal filter in that line, perhaps?

holding_tank_bubbles.jpg
 
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Jan 11, 2014
4,061
Sabre 362 113 Fair Haven, NY
Sounds like a good plan.

If you can remove the vent hose from the tank, then use the hose to blow out the vent hose, just be sure to suck the water out afterwords. A shop vac can suck it out. You may need an adapter to fit the hose. Shop Vac makes a "Micro Cleaning Kit" that has an adapter that should fit. I use it in the fall when winterizing to blow out the water lines.

A simple strap wrench will tighten the cap.
 
Dec 2, 1997
7,363
- - LIttle Rock
While filling with water, I scrubbed the vent screen with a wire brush and doused it with soap to bubble-test it as continued water input led to air displacement. But instead, a quick burst of liquid released from the vent and then nothing more...no bubbles.
If you knock the screen out of the vent thru-hull (screens created more problems than they prevent because they get clogged with dust , pollen and corrosion), you may not need to replace the thru-hull unless you want to upgrade to a larger diameter vent line (easy to do, thanks to a li'l gizmo called the Uniseal UNISEAL )

You can remove the vent line from the boat to flush it out if you want to, but I don't think that'll be necessary 'cuz 99% of vent line blockages are in two locations: the vent thru-hull and the other end of the vent line--both that end of the hose and the vent fitting on the tank, due to waste spilling into it when the boat is heeled.

Fabricate a wrench to close the inspection port with enough torque to ensure the gasket is really squeezed down. Add more thread tape.
Don' do dat! You'll damage the cap or the tank. Replace the gasket and o-ring instead. They're rubber...rubber dries out...so they need replacing every few years.

#4. Don't even THINK of routing the vent to the coach roof OR putting a filter in it! Vent lines need to be a short, straight and HORIZONTAL (level) as possible..NO SAGS! You have my book..read the part about vent lines.

As much parental pride as I have in K.O., there's something MUCH better today: No-Flex Digestor Noflex Digestor

If we need to discuss all this in more detail than is practical in a forum, send me a PM and we can pick a mutually convenient day/approx time to spend 30-40 minutes on the phone.

--Peggie