Tuesday, October 3, 2023


RV holding tank treatments: What’s best for the environment?

By Russ and Tiña De Maris
Stroll the aisles of your favorite RV accessories store, or even Walmart. When you get to the RV holding tank treatment shelves, what do you see? Row upon row of bottles and boxes. Every one of those potions promises less smell, and the best outcome for your “outflow.” As RVers, we love nature, and often, when we dump tanks, we’ll have an effect on the environment. So when dumping your tanks, how can you avoid “dumping” on Mother Nature?

It’s a question that not only concerns RVers. It’s also important for RV park owners who may have a septic system. And if you dump your wastewater at home, if you own a septic system, you should be very concerned. Put the “wrong” stuff in your septic system, you could be looking at a system failure. That could spell out a costly mistake, as it could literally wipe out your leach (drain) field.

State park RV sewage raises – not a stink – but questions

What’s safe for septic systems and the environment? It’s a question raised by researchers with the University of Minnesota’s Onsite Sewage Treatment Program. Dr. Sara Heger is one of them, and also an instructor with the program. Last fall, Dr. Heger published an analysis of RV holding tank treatment products. We’ve reviewed that report, and spent some time interviewing her about those findings.

Back in 2019, Dr. Heger’s team investigated septic systems at two Minnesota state parks. They sampled wastewater at both parks that was generated by the RV dump stations – no other wastewater was included. When they compared the dump station wastewater with typical domestic wastewater, the differences were huge. Here’s one example.

A little bit of a chemistry lesson

A key factor to keeping a septic system and the environment happy is holding down the biochemical oxygen demand (BOD). To break down solid wastes, plenty of oxygen is required. Too little oxygen, the waste material doesn’t break down. And at the far end of the treatment system, too high a BOD translates to harm to the environment. If a lot of treated effluent makes it out to, say, a lake, river or stream that has too little dissolved oxygen, it can harm aquatic life. If the oxygen level reaching a septic system leach field is low, the life of the field is reduced – a costly problem.

The figures for BOD in what normally flows into a sewage treatment system from most homes is around 140 to 200 milligrams per liter. Of the two parks where RV wastewater was tested, one showed a BOD of 1280, the other, a whopping 1530 – almost eight times the “normal” amount. Other indicators were way up, too. Phosphorous levels were four-and-one-half to seven times above normal. Out in the environment algae growth is accelerated by phosphorous, leading to low oxygen levels in water, harming aquatic life.

Dr. Heger says the elevated levels of BOD and phosphorous (as well as other chemical and biological factors) in the wastewater could have been caused by the concentration of stuff coming out of RV holding tanks. After all, not many RVers do laundry in their rigs, and showers are typically shorter than “at home.” But the group wondered if something else were at play. Was it possible that RV holding tank treatments were having an adverse effect on RV wastewater?

Four popular brands compared

To explore the question, Dr. Heger picked four popular RV holding tank treatment products. They were:

  • Happy Campers Organic RV Holding Tank Treatment
  • Thetford Aqua-Kem Original
  • Walex Porta-Pak Holding Tank Deodorizer with Sunglow Scent (TOI-91799)
  • Walex Bio-Pak Natural Holding Tank Deodorizer, Alpine Fresh Scent (BOI-11530)

These four were chosen based on their Amazon.com customer review ratings, indicating popularity among RVers.

To analyze how these various RV holding tank treatment chemicals might affect sewage treatment systems, a simple but effective test was done. One at a time, a single “dose” of the respective chemicals was added to a five-gallon bucket of water, and samples were taken. These samples were sent to an outside testing lab for analysis.

To keep things orderly, in terms of concentration, a volume of 40 gallons was figured to represent the typical RV black water tank. Researchers used a dilution calculator to figure what the concentration of the treatments would be like in a 40-gallon tank versus the five-gallon test batch.

And the results?

CLICK TO ENLARGE. University of Michigan Onsite Sewage Treatment Program

So what were the results? We’ve included a copy of the chart showing the results. The chart includes the test results from the two state parks we mentioned earlier. Then in the third results column (from the left), a reference value is given – this for typical domestic sewage. Finally, the last four columns to the right show results from each of the four tested products.

Interestingly, the products which produced the highest oxygen demand were Aqua-Kem and Walex’s Porta-Pak. Aqua-Kem contains formaldehyde, which use is banned by some states. The Walex Porta-Pak contains Bronopol. That chemical is a formaldehyde releaser – a chemical compound that slowly releases formaldehyde as it decomposes. A study done for the Washington State Department of Transportation – which operates a number of highway rest stop dump stations – showed formaldehyde could harm bacteria helpful to septic tank systems.

Quoting from Dr. Heger’s report, “The Happy Camper product had the lowest levels of all contaminants evaluated.” The report did express concerns that it was acidic, and could upset bacteria needed for waste treatment. As to Aqua-Kem, the report notes that it “had a very high value of BOD and COD [chemical oxygen demand] which indicated it will add a considerable load to a wastewater treatment system if used by most RV users at a particular dump station.”

And the Walex products? They “were relatively low in all contaminants evaluated, aside from the phosphorous of the Bio-Pak at 57.5 mg/L indicating it will add a considerable phosphorous load to a wastewater treatment system if used by a majority of RV users at a particular dump station.”

“Holding tank” or “septic tank”?

When it comes to the various kinds of RV holding tank treatments, we’ve heard from a couple of different camps. One argues that using a bacterial/enzyme treatment will help break down the solids in an RV holding tank. The opposing side says, these are “holding tanks” not “septic tanks,” and rules the idea beside the point. We asked Dr. Heger about this: Might there be an advantage to an enzyme-based RV holding tank treatment? She told us that there are “no third-party proofs” that holding tank enzymes really do break down wastes.

And when it comes to RV holding tank treatments, what’s the best in her mind? To Dr. Heger, the best holding tank treatment is NO holding tank treatment. This immediately conjured up a picture of a popular holding tank treatment advertisement from years back. The RVing wife, frantically holding on to the entry door handle, while her husband attempts to push her into the “smelly” RV. Does everyone have a stinky RV “loo”?

Do you really need it?

Here’s our experience: We live in our travel trailer, 24/7. Those 24/7s include several 100+ degree weeks in Arizona. In the last two-and-a-half years, we’ve had ZERO odor problems – and we hadn’t been using any sort of treatment. That is, until we pulled up stakes a few weeks ago after sitting stationary for a number of months. We then did get a few whiffs of foul black water odor. We wonder if perhaps the “whole lot of shakin’ goin’ on” might have stirred up an otherwise happy holding tank. In any event, of late, the odor has rapidly diminished.


Was our no-more-stink associated with the single packet of Walex Bio-Pak that we chucked down in the tank a week ago? My own suspicions say, “Probably not.” I’m more inclined to believe that the rotating roof vane atop my black water tank vent is doing a better job. With the wind blowing and the vane doing its job of sucking those foul odors out of the tank, there’s a whole lot less that can now come back up while we hit the “flush pedal.”

If you’ve got stink in your RV, check this out too: Between flushes, is there a small amount of water in your toilet bowl? If there isn’t, it’s likely your toilet bowl seal has failed – allowing those horrible vaporous emanations to assault your nose. With the proper roof and bowl gear, you might not need RV holding tank treatments at all. Mother Earth will tank – er – thank you.

Update history: Removed statement that high levels of phosphorous could damage septic drain fields. 8/23/201


Holding tank tips for the stationary RV
RV Education 101: Keep holding tank odors out of the RV
California bans formaldehyde as holding tank chemical

360 Siphon Roof Vent Cap on Amazon


Russ and Tiña De Maris
Russ and Tiña De Maris
Russ and Tiña went from childhood tent camping to RVing in the 1980s when the ground got too hard. They've been tutored in the ways of RVing (and RV repair) by a series of rigs, from truck campers, to a fifth-wheel, and several travel trailers. In addition to writing scores of articles on RVing topics, they've also taught college classes for folks new to RVing. They authored the book, RV Boondocking Basics.


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10 months ago

From day one, 2 1/2 years, we’ve used “Happy Camper.” No fake cover-up perfume, citrus, Greyhound bus lav smells, – Actually NO smell at all! Better yet, I’m not at my kitchen table acting all mad scientist, mixing all kinds of laundry, dish-washing, industrial janitorial, vinegar, coca-cola, radioactive waste, whatever else crap because someone on the internet said it was the greatest! In both gray and black tanks, Happy Camper simply works.

Don Waggoner
10 months ago

I clean tanks as a business. 2 things I do and recommend, get a small flip top garbage can and waste bags (Walmart) put all toilet paper in can (can use soft less expensive toilet paper). Then for tank additives, pine pinsol(40oz) and 1/2 cup Calgon bath beads in 1 gallon jug. Bath beads first, then pinsol, then fill with water. We have been in Arizona since January and no stink any time. Also I recommend having tanks cleaned every year or two .

10 months ago

I use a 360 deg rotating roof vent and add Rid-x to both tanks thru the sink drain – P-trap and toilet. Rid-X is approved and preferred for holding tanks and septic systems. We haven’t had any problems with odor or clogging either. (About 20 years!)

Ron L
10 months ago

I too am among those who never use any black tank additive but only liquid laundry soap and Calgon when we travel. When stationary (and we are for five straight months), lots of water is our only solution…. I repeat… lots of water. I have modified our black/gray drain by adding a third gate that allows me to transfer the soapy gray water over to the black tank. I typically let the tanks get about 2/3rd full and then empty the black tank first. I’ll close off the third gate, open the gray tank gate and then open the black tank gate. The tanks will equalize with the gray water. I’ll then close the gray tank gate and open the third gate allowing the black tank to once again drain. I’ll repeat the process two or three times all the time with the black tank rinse turned on. Once most of the gray tank water is gone, I’ll close the black (allowing the rinse to put clean water in it) and open the gray and the third gate allowing the gray to completely empty. After about 5 minutes

Ron L
10 months ago
Reply to  Ron L

I’ll stop the rinse water leaving several gallons of water in the black tank. This process has worked very well for me with no problems with either tank and the sensor always work as designed. Occasionally when emptying the black, there will be a slight odor, but only outside…never inside. It’s my opinion, after using this process of the laundry soap and Calgon while traveling and the third gate while stationary, that using ANY black tank additive is a total waste (pun intended) of money. I always pass on this advice to any who ask for my opinion in hopes that it will provide the same success that I have encountered.

Duane R
1 year ago

I made some reservations at some Washington State Parks a few days ago. Their site says that campers are not to use tank additives, as it is wreaking havoc on their septic systems.

Tom H.
1 year ago

Check out Camp Champ

2 years ago

A device added to the top of the vent does nothing. Other than the brief instant the toilet is flushed, the vent is the only opening. In order to draw gas/air from a holding tank with one opening would require creating a vacuum in the tank and that isn’t going to happen.

Bill N Stacey
2 years ago

Bio/Geo Method Works For Us : )

2 years ago

We spend months at a time in our motorhome, and rarely use any treatment. The secret is oxygen – which is 20% of normal air. When there is adequate ventilation of the tanks, and normal use with fresh water (and air) entering several times a day, the contents stay aerated well enough that aerobic bacteria predominate in the tanks, and they don’t produce smells. If there is not enough ventilation, anaerobic bacteria take over and they do produce smells. If you are getting bad odors, the most likely cause is a blocked sewer vent or not enough use.

2 years ago

The only time I get odor is when it is time to empty the tank which usually follows when I get that ‘burp’ when flushing. I have tried things to do control odor but as I say it only happens when ready to dump. Now the only thing I dump in is a box of baking soda. It makes the bottom of the tank slick so things hopefully won’t stick. Been living in it since 2004.

2 years ago

We have been full-timing for about 10 years. We normally don’t use any treatment. Usually, if it is very hot weather (95°+) we may get some aroma. One treat of RV Digest It, or whatever else is under the bathroom sink usually does the trick. This happens once or twice a year. We have had the swivel type tank vents in previous coaches, but we are currently using whatever Tiffin installed up there with the same results.

2 years ago

12 years fulltime (200K miles), the last 9 years with virtually no tank treatments, & no odor problems. I replace the toilet valve seal every year or two & use a Siphon 360 vent cover.

2 years ago

I started using the Geo method and due to availability of Calgon and cost of Dawn switched to just using detergent. Probably don’t even need that.

Ron L.
1 year ago
Reply to  Zeet

For the record, Dawn is NOT a prescribed element for the GEO method… laundry detergent is. I’m not sure where/when/who the use of DAWN seemed like a good idea, but it really doesn’t apply to this method.

Rolling Coal
2 years ago

We’ll be parked for about a month at our current location. I’m going to experiment while we’re here and not use any chemicals in the black tank, only the flush system between fills.

2 years ago

We are full timers and have not used any treatment in the black tank for a number of years now. Here are a few non scientific observations:

  1. As mentioned in the article keep the toilet seal in good condition.
  2. Having used both the rotating vane and the Lippert 360 Siphon vent I think the siphon vent works much better at controlling odors especially when stationary for a while.
  3. When traveling, close the bathroom roof vent. Depending on the location of the black tank vent in relation to the roof vent odors can be sucked into the bathroom.
  4. When possible after emptying the black tank, close the valve and use the tank flush system to mostly fill the tank and then empty it again. Important – Use a timer so that you don’t accidently overfill the tank!!!

This seems to work for us and we don’t have any black tank odor problems.

Oliver Quibble
2 years ago

We have used Unique RV Digest-It for all our years of fulltiming (2015). Take the time to read about their products. Their customer service is top notch too.

2 years ago

I use a vinegar (5%) flush when I return to home base. Fill black tank 1/2 way with water, add a gallon jug of vinegar, let soak. Then, using built-in flushing system, flush the whole system out.

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