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Old 13-04-2020, 12:25   #1
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The dreaded holding tank odor!

Hi Folks,

I'm new to the site, but have certainly used your collective wisdom in the past when google searching! First of all, I do want to preface my post by saying I've read Peggie Hall's book, so I'm not completely ignorant on the topic, yet my problem persists. My basic setup is a 41' Silverton with a 72 gallon holding tank. There are two raw-water heads, but I just use the one in the aft cabin (the other head doesn't work). I live aboard, so the system is in constant use.

So my problem is described in the title and it's something I've experienced since I bought the boat in October 2019. Let me break down the problem into two components. The first is the holding tank odor I experience INSIDE the boat. It's relatively minor, and is definitely coming from the vicinity of the tank itself. I started by replacing 3 waste hoses that I determined permeate smell by using the wet paper towel trick. However, there is still one hose (one of the two vent lines) that does emit odor, but I haven't replaced it yet due to access (I can't get to where it connects to the thru-hull without taking out the hot water heater). The smell inside is better than before, but still slightly noticeable. Short of replacing that hose, though, I'm hoping the smell inside can be minimized by addressing the second part of my issue:

The smell OUTSIDE the boat is bad. I often walk by the stern of my boat and catch a whiff of sewer gas, and keep in mind the waste thru-hulls are toward the bow. I've never walked by another boat on my dock and noticed a smell, so that leads me to believe I've got other issues (oxygenation, etc) going on in the holding tank. Let me tell you what I have tried to do to address it. At the end of last year I pumped out the tank, flushed it with fresh water, and pumped it again. The previous owner was using the West Marine blue chemical deodorizer, and I wanted to switch to a biological method. Per Peggie's book, I have been using Raritan KO in combination with Odorlos, as directed. I realize you're not supposed to combine two holding tank products, but since KO is a dose of aerobic bacteria and Odorlos supposedly encourages good bacteria to grow, I didn't think this was an issue (correct me if I'm wrong!). I don't, however, dose them at the same time, usually a day apart. Another thing I did at the same time I flushed the tank, was forced fresh water through a hose into the two thru-hull vents, just in case one was blocked. There are two 1-inch vents on opposite sides of the boat.

So this leaves me scratching my head a bit (no pun intended!). I've thought of converting the head to fresh water, but from my understanding, raw water is only a problem when it's allowed to sit in the intake line or the head, the organics decompose, and a rotten egg smell is noticed. I have no odors coming from the head itself, as it's used daily. So would this even help the issue?

My other thought is improper ventilation, but as I've said, I shot high pressure water into both vent thru-hulls to clear any blockage, and both seem to be adequately sized.

My last thought was discontinuing the use of either KO or Odorlos in case combining the two is somehow exacerbating the problem, but this doesn't seem to make sense to me.

Anyway, I apologize for the long post, but would really appreciate anyone's advice to help me through this!

-Matt
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Old 13-04-2020, 14:01   #2
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Re: The dreaded holding tank odor!

Hi Matt...welcome to Cruisersforum!

Apparently you have the first edition of my book, which--not surprisingly, since it was published in 2003--has a considerable amount of outdated info and product recommendations in it.

You'll go a long way in solving your odor problem if you do a couple of things...starting with, that smelly vent line must be replaced. Since it's gonna be a major PITA to do that, let's make the most of the access to the vent thru-hulll by replacing it with an open bulkhead aka "mushroom" thru-hull....and if possible, straighten and shorten the vent line too. That'll allow a LOT more air exchange with the gasses in the tank, which will go a long way in improving the necessary aerobic environment in the tank.

When I wrote the first book, K.O. and Odorlos were the best tank products...and they still work very well as long as the tank is well enough ventilated to be aerobic, 'cuz K.O. can only function aerobically when it is.

But there's a tank product now that doesn't need nearly as much oxygen: Noflex Digestor Noflex Digestor Everyone who uses it raves about it.

If replacing the vent line and the vent thru-hull and switching to NoFlex doesn't entirely cure your odor out the vent, upgrading the vent line to 1"--which will require replacing the existing vent fitting on the tank, which thanks to a li'l gizmo called the Uniseal UNISEAL is very easy to do if you have enough room above the tank to use a hole saw to cut the new hole in the top of it. The existing vent fitting can be sealed with a threaded plug wrapped in plenty of Teflon tape. We can discuss that later if it turns out to be necessary.

You're welcome to give me another shout here or privately if you still have questions...I'm glad to help!

Btw and fwiw, you'll find the link to the updated version of my book in my signature...just click on the title.


--Peggie
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Old 13-04-2020, 14:16   #3
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Re: The dreaded holding tank odor!

Although my opinion doesn't carry as much weight I'll definitely second Peggy's suggestion on Noflex Digestor. Like the OP I replaced hoses and did all the other suggestions, as well as trying a half dozen other tank treatments and still had the vague smell I couldn't get rid of. Noflex was like magic, in a couple days I could literally take the cap off the holding tank and there was almost no smell inside the tank, which of course meant absolutely no smell outside the tank.
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Old 13-04-2020, 14:58   #4
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Re: The dreaded holding tank odor!

Quote:
Originally Posted by peghall View Post
Hi Matt...welcome to Cruisersforum!

Apparently you have the first edition of my book, which--not surprisingly, since it was published in 2003--has a considerable amount of outdated info and product recommendations in it.

You'll go a long way in solving your odor problem if you do a couple of things...starting with, that smelly vent line must be replaced. Since it's gonna be a major PITA to do that, let's make the most of the access to the vent thru-hulll by replacing it with an open bulkhead aka "mushroom" thru-hull....and if possible, straighten and shorten the vent line too. That'll allow a LOT more air exchange with the gasses in the tank, which will go a long way in improving the necessary aerobic environment in the tank.

When I wrote the first book, K.O. and Odorlos were the best tank products...and they still work very well as long as the tank is well enough ventilated to be aerobic, 'cuz K.O. can only function aerobically when it is.

But there's a tank product now that doesn't need nearly as much oxygen: Noflex Digestor Noflex Digestor Everyone who uses it raves about it.

If replacing the vent line and the vent thru-hull and switching to NoFlex doesn't entirely cure your odor out the vent, upgrading the vent line to 1"--which will require replacing the existing vent fitting on the tank, which thanks to a li'l gizmo called the Uniseal UNISEAL is very easy to do if you have enough room above the tank to use a hole saw to cut the new hole in the top of it. The existing vent fitting can be sealed with a threaded plug wrapped in plenty of Teflon tape. We can discuss that later if it turns out to be necessary.

You're welcome to give me another shout here or privately if you still have questions...I'm glad to help!

Btw and fwiw, you'll find the link to the updated version of my book in my signature...just click on the title.


--Peggie
Hi Peggie,

Thank you so much for responding so quickly! I was hoping the expert herself would weigh in. I will definitely read the latest edition of your book - rookie mistake on my part downloading the old edition.

Funny, I had been wondering if there was a product you could add that would release oxygen into the tank... I even thought about experimenting with hydrogen peroxide. I did a little research into Noflex, and it is exactly what I was thinking of. The MSDS says it's mostly disodium carbonate and hydrogen peroxide, which when mixed together create sodium percarbonate, the active ingredient in Oxiclean powder. I'm a microbiologist by training, so I had to dig deep to figure out how it worked. Based on your recommendation and the science, I'm excited to give this a try! It would be interesting to see if Oxiclean would be a suitable (and cheaper) alternative, but there might be other chemicals (perfumes, detergents) in it that may interfere with the growth of aerobic bacteria. Alas, an experiment for someone else to try!

Anyway, thank you again and I will report back in this forum when I'm able to try out Noflex.

Cheers!

-Matt
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Old 13-04-2020, 14:59   #5
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Re: The dreaded holding tank odor!

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Originally Posted by redneckrob View Post
Although my opinion doesn't carry as much weight I'll definitely second Peggy's suggestion on Noflex Digestor. Like the OP I replaced hoses and did all the other suggestions, as well as trying a half dozen other tank treatments and still had the vague smell I couldn't get rid of. Noflex was like magic, in a couple days I could literally take the cap off the holding tank and there was almost no smell inside the tank, which of course meant absolutely no smell outside the tank.
Thanks, Rob! Glad to hear you had a similar problem and it worked for you.

-Matt
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Old 13-04-2020, 18:27   #6
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Re: The dreaded holding tank odor!

Another vote for the magic of Noflex Digestor. My last boat black tank vent was located near the cockpit, with resultant smells wafting through when one was in party mode with multiple people aboard using the head.

I had planed all the work and procured the materials to move the vent and vent hosing, but two days in with Noflex Digestor as per the supplied instructions, the issue was forever resolved, without any mechanical changes.
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Old 13-04-2020, 20:32   #7
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Re: The dreaded holding tank odor!

Noflex does something more that I don't THINK Oxyclean can do: dissolve sludge and the buildup on tank walls.


--Peggie
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Old 14-04-2020, 04:23   #8
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Re: The dreaded holding tank odor!

Matt, I don't think you mentioned having vent filters... or having changed the filters, if you have them. Peggie will tell you vent filters can cause the problem their meant to solve, but... we've not ever had inside odor issues on any of the three boats we've had that used vent filters... and the vent filters do seem to eliminate external/outside holding tank odors. Until they need replacing. Ours usually last 3-4-5 years or so...

We used KO before, since whenever Peggie introduced it actually, but have recently switched to Noflex. We've never had head odors inside the boat -- even when we haven't used one of those products for a while -- but I hope they at least manage potential sludge build-up over time. That said, we recently replaced our holding tank with a new one, and the sludge build-up in the old one was pretty serious... even after 4-5 years of KO and 7-8 years of Noflex.

Peggie's the authority for head and odor issues, but FWIW, there's also a Silverton owners club out there, members supporting members especially about other issues (including replacing holding tanks). Modest annual fee, mostly to fight spam.

-Chris
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Old 14-04-2020, 07:15   #9
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Re: The dreaded holding tank odor!

We've never had head odors inside the boat -- even when we haven't used one of those products for a while --


When it comes to odor INSIDE the boat, it doesn't matter what you use in the tank--or whether you use anything--because the tank is never the source of odor INSIDE the boat unless it's leaking. If you have odor inside the boat, it has to be from another source--permeated hoses and/or a wet bilge in serious need of a REAL cleaning are the most common sources.


--Peggie
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Old 14-04-2020, 07:35   #10
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Re: The dreaded holding tank odor!

Peggy doesnt like them...but I fixed the problem with a vent filter.
About 12" of pvc pipe with hose barbs at each end.fill with activated charcoal with foam disc on each end to keep the the charcoal inside and fit into the vent line.
When the smell reappears, replace the charcoal.
Takes about an hour to fabricate, cost less than $10.
Bob
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Old 14-04-2020, 08:46   #11
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Re: The dreaded holding tank odor!

Quote:
Originally Posted by Navillus_83 View Post
Hi Folks,

I'm new to the site, but have certainly used your collective wisdom in the past when google searching! First of all, I do want to preface my post by saying I've read Peggie Hall's book, so I'm not completely ignorant on the topic, yet my problem persists. My basic setup is a 41' Silverton with a 72 gallon holding tank. There are two raw-water heads, but I just use the one in the aft cabin (the other head doesn't work). I live aboard, so the system is in constant use.


Etc.


-Matt

And for odors inside the tank, I used the Head Mistress's recommendation to add Downy (right product, Ms. P?) fabric softener. Had to replace hoses after we bought the boat, which entailed requiring opening the tank to scoop out the bit that couldn't be handled by the pump out. A few days before, we bought out the store (I know, I know, HOARDER!! but at least it wasn't toilet paper) and did a series of fill and drains. When I popped the inspection port open, I wouldn't say it was lovely, but it wasn't too bad (can't believe I just said that). The only problem Ms. Hall neglected to mention in her book was years later, you'll still associate Downy with holding tanks, which makes doing laundry a bit of a challenge... LOL?
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Old 14-04-2020, 09:07   #12
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Re: The dreaded holding tank odor!

I installed a fish tank aereator with the tube going into the top of my holding tank. While dockside it flows fresh air through the tank and out the vent. I have never had any odor inside or outside since. Problem solved.
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Old 14-04-2020, 09:29   #13
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Re: The dreaded holding tank odor!

I've done Peggy's suggestion of replacing the vent line with a wider (1") hose and a opn, or mushroom head, thru hull. Solved my problems too. Listen to the woman, she knows her...stuff!
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Old 14-04-2020, 10:05   #14
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Re: The dreaded holding tank odor!

Our boat came with two vents [spaced apart] on the large aft head holding tank— each exiting opposite sides of the boat. This seems to create enough air flow in the tank to curtail anaerobic conditions as we have never experienced odors from the tank.

Details of this arrangement:

The tank vent fittings exit opposite sides of the tank top. [port and starboard] This allows air flowing through the two fittings to contact maximum liquid surface area in the tank.

The through-hull vent hose fittings are also on opposite sides of the boat. [port and starboard]

The 3/4" vent hoses run from the tank fitting to the opposite side hull vent fitting. [i.e., port tank vent hose is connected to the starboard hull fitting, and visa versa.]

This crossed hose arrangement reduces the chances of effluent in a full tank running out a vent line when heeled... [When heeled, the low side tank vent fitting exits the boat on the high side...]

This may not be practical for some installations, but it does seem to help promote a healthy aerobic holding tank environment for us.

FWIW

Cheers! Bill
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Old 14-04-2020, 10:28   #15
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Re: The dreaded holding tank odor!

Thank you all for your input! I should have mentioned, I don't THINK the tank odor is due to improperly sized or installed vents. They're 1.25" (outer diameter) PVC installed on opposite sides of the tank exiting the hull on opposite sides connected to open thru-hulls, and there are no excessive bends or turns.

As for the suggestion of vent filters, I would rather try to see if I can solve the odor problem rather than just use filters to absorb it. Also, good suggestion Sailshabby, about doing a good tank clean with downy. I will be getting my shipment of Noflex soon and I'm hoping this, in addition to replacing the one smelly vent line, will go a long way!

-Matt
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