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

August 06, 2021

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?

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.