I mentioned in an earlier post from a few weeks ago that I would explain what happened with our black tank, so here goes!
WARNING: This post will discuss the maintenance and care of the black holding tank in an RV/Bus/Motorhome, that is the tank that holds human waste ie. poos and wees! DONOT read any further if the subject offends.
We had emptied the black tank before we took the van in to have a new loo installed, which highlighted not only a bit of rot in the floor but we were reliably told that our black tank was definitely not empty. Oh no, have we got the dreaded “poo pyramid”?
No, we do not have the pyramid of poo which forms when the vehicle is stationary for long periods of time and not enough water is used. There is a large resource of blogs/videos/articles available to read about this anomaly on YouTube and by asking Mr Google. In our case, on inspection, that is by looking down the toilet into the tank with a torch, it looked as though the base of the tank was covered in a layer of something that almost looked like compacted toilet paper. On further investigation and many hours of research later, I realised that this was in fact what is called Struvite.
What is Struvite? It is defined as a phosphate mineral crystal with an elemental composition of magnesium, ammonia, and phosphate that forms in water and is a completely natural process. In simple terms its the black tank equivalent of kidney stones.
Magnesium is a byproduct of hard water, Ammonia is a byproduct of urine and urea and phosphate is a major element of organic matter, food and detergents. They come together in crystal formation to form a rock like substance that then lines the tank and pipes.
Struvite causes a scale-like formation in pipes in sewage and waste water treatment plants, heat exchangers, and many applications in the marine environment and RVs to name a few. Struvite can prove to be a major problem for Recreational Vehicle (RV) owners where hydro-flushing, mechanical cleaning, or the use of acids are needed to rid of the buildup that can clog up the pipes and systems as well as rendering those monitoring sensors as ineffective.
It can also occur in household toilets and pipework, especially in hard water areas and is noticeable in toilet bowls, it looks like there is calcification buildup in the base of the toilet bowl.
I spent many, many, hours reading, watching videos and researching the many many articles on the subject, there are a huge number of YouTube videos on the causes, treatment and removal of struvite from black tanks in particular. Most of them seemed to require the need to employ someone who specialises in basically water blasting the inside of the tanks – this seems to be more of a specific job in the USA as I’ve never heard of anyone doing this in NZ. Or we could purchase a special back flush valve attachment and the rest of the gear and do it ourselves however this is more suitable to waste systems where the pipework is in a direct line from the tank to the outlet, ours is not as it twists and turns.
In the end I contacted a company in NZ that supplies a product called Rydlyme, this to me seemed to be the best, most efficient, effective and safe method to remove struvite. Rydlyme is non-toxic, biodegradable, and can be safely disposed of in sewers. It’s not cheap but we decided to go ahead and give it a go. The company were extremely helpful and talked me through its use and effectiveness, I was most impressed with their helpfulness and efficiency.
We had 20litres of Rydlyme delivered for when we headed down to the van before returning it to the repair shop. We put the Rydlyme into the tank with a few litres of water. It’s most effective application, we were told, is to be continually pumped and cycled through, as in it would take 15-30minute to successfully complete the task, however, it would work just as well by being left to sit in the tank for at least 24hrs and as we were heading to Antony’s for the weekend, we could safely leave it standing for around 48hrs as that is just how timing worked for us.
On our return, we emptied the tank and were amazed at how much extra liquid came out, as in probably close to 80litres. Remember the tank was supposedly empty and we had only put in the 20litres of Rydlyme with a few litres of water. It did not smell nor was it offensive in any way but it certainly removed all the struvite in the tank and the pipework. A few extra litres of fresh water were put through to rinse out the tank, what an excellent result.
The next thought is how can we prevent this from occurring again? The answer is water, make sure you use plenty of water when flushing to dilute the contents, especially as uric acid production is apparently increased, by men in particular, as they age, as well some medications affect uric acid production, and of course what you eat and drink. A water softener is also a good additive to use. There are plenty of recipes for what is called the Bio-Geo method of treating your waste tanks, each one slightly different in the products they use depending where in the world you may be. It is up to you to choose your own methodology and recipe. The thing to remember is that your black tank is a holding tank NOT a septic tank, therefore you need to be able to flush the tank out cleanly and effectively (ie. make it slippery) rather than be concerned about decomposition.
Why did this occur now and not before? Well, that’s a function of three major factors;
1. We haven’t been moving as much as usual in the past 18 months having been in the UK for 6 months, then at Shakespear for another 3 months and sitting still for long periods whilst housesitting.
2. We would usually let the tank get fairly full before emptying so as to create a good volume, or wooosh when emptying as this is what is recommended. But recently we have been more frequently using a tote tank to decant the tank into (to negate the need to drive the RV to a dump station) which takes around 40litres at a time and as it’s done every week the tank does not get full enough to empty completely.
3. We normally give the tank a good rinse out or back flush after emptying at the dump station but we’ve been a bit slack on this of late especially when using the tote tank. We would usually attach a hose at the dump station and pass the hose through the toilet window and flush the tank out by filling the tank through the open valve in the toilet NB. but only if there aren’t others waiting to use the dump station – we don’t want to be one of “those” people!! Note to self: use lots of water especially to rinse out the tank after emptying.
I usually always put a few litres of water into the bottom of tank after emptying, I think I may have been a bit slack in this regard as well (trying to save water and all that). This prevents any residue drying out and hardening but adding water also starts off the next lot of dilution and decomposition. Trying to save water is silly really as we don’t really use that much water particularly if you compare how much we would use in a week compared to an average household. Our water tank holds around 280litres of water and we would use around a tank full for the two of us in 10-14 days depending on how frugal we are being, whereas the average person in NZ uses between 140-170litres per day (according to Watercare Auckland).
It is a good job well done, and one we hope NOT to have to do again so long as we maintain the tanks correctly. I hope this has been of some help to some of you.