Partial? holding tank system - is that a thing?

[ylop]

I still have a modest understanding of basic chemistry from my time in research many, many years ago.

Then you should know to try an experiment before dismissing its empirical results! I’m suggesting to the OP that I had similar issues which due to bends in the paperwork I failed to mechanically rod, but I solved with the one acid I could buy in a remote location in large quantities cheaply. I was surprised how effective it was which is what lead to my hypothesis that the gas was having some effect.

You should be able to get Hydrochloric acid in many places at reasonable strength, probably 7-10%.

Indeed, had I been close to a big town with trade suppliers I would probably have gone their first. But I was in the middle of nowhere with just a small corner shop.

Many supermarkets stock it.

Not in the UK. If you were lucky then one of the huge 24h ones MIGHT have it.

Unless people are shitting carbonate bricks I fail to see what hydrochloric acid / vinegar ( acetic acid) or Diet Coke will do in any meaningful time frame to a blockage of solidified excrement and paper.

Of course, but if you’ve actually encountered the problem and checked out with many others who have then you’ll discover that sheets of crystalline material form on the inside of the tank then fall off. You don’t need to dissolve all that you need to break it up so the pieces are small enough to fit out the pipework. It could be shit and paper but you’ll find people who don’t use paper, or have been reliable using their system for years when they get a problem and those brave enough to get the marigolds out often find chunks of crystalline stuff.

 

[dunedin]

.....

And to confirm, when the seacock is opened at sea the tank will drain, I assume through physics and not black magic?

Or use a pump out facility.

The tank should be above both the seacock and above the waterline. Then gravity does its work.

(If not blocked by solid objects)

 

[Irish Rover]

It's amazing how many experts we have on YBW when it comes to talking shit .

 

[wonkywinch]

I keep the old joker valve on the chart table (thoroughly cleaned!). Anytime someone new comes onboard, I show them the tiny bit of rubber their waste has to pass through as a reminder how delicate the system is on a boat.

A friend did question me on how is "output" often resembled the size and shape of a babies arm would fit through that.

 

[Tranona]

Indeed I’m more familiar with diverter valve setups.
I’ll feed all this back, thank you!

And to confirm, when the seacock is opened at sea the tank will drain, I assume through physics and not black magic?

Or use a pump out facility.

Diverter valves are more commonly used on pumped systems with a below the waterline tanks - very different from the simple gravity system. The former are more commonly retrofitted because few older boats have space for gravity tanks. More modern boats , particularly those built after tanks became compulsory were designed with space to fit a tank, either in the loo compartment or in a cockpit locker. The only benefit of a diverter is that it allows direct discharge to sea while the tank is full. Downside is another potential blockage point.

 

[Chiara’s slave]

I don’t see how opening the seacock will drain the tank, unless the tank is fitted high up in the boat. Wouldn’t it normally be at least partially below the waterline? Ours is, and our boat sits higher in the water than 95% of other boats. We have a diverter valve and a hand pump to discharge if well out to sea. Normally we use a pump out facility in the harbour.

 

[johnalison]

Diverter valves are more commonly used on pumped systems with a below the waterline tanks - very different from the simple gravity system. The former are more commonly retrofitted because few older boats have space for gravity tanks. More modern boats , particularly those built after tanks became compulsory were designed with space to fit a tank, either in the loo compartment or in a cockpit locker. The only benefit of a diverter is that it allows direct discharge to sea while the tank is full. Downside is another potential blockage point.

We have a diverter system. The only likely reason for a blockage in the main line is build-up of scale in the pipe from inadequate pumping. We have never experienced a blockage from the holding tank and I would be averse to having all my waste through the tank. There are times, such as when berthed in Salcombe on buoy or anchor, when it is desirable to use the tank for solid waste for a few days, and the ability to shed urine directly (along with all the swimmers and fish) is useful. Our tank has the capacity of just over 200 pumps and could well be overloaded in two or three days.

 

[Tranona]

I don’t see how opening the seacock will drain the tank, unless the tank is fitted high up in the boat. Wouldn’t it normally be at least partially below the waterline? Ours is, and our boat sits higher in the water than 95% of other boats. We have a diverter valve and a hand pump to discharge if well out to sea. Normally we use a pump out facility in the harbour.

Well, they are above the waterline in boats designed to have them - that is the whole point, and why it is often difficult to retrofit into older boats which do not have space for an above the waterline tank. However I fitted one of decent size (30l) to my old Eventide \nd could fit one to my GH as there is space to get about 45l in.

 

[wonkywinch]

I don’t see how opening the seacock will drain the tank, unless the tank is fitted high up in the boat. Wouldn’t it normally be at least partially below the waterline? Ours is, and our boat sits higher in the water than 95% of other boats. We have a diverter valve and a hand pump to discharge if well out to sea. Normally we use a pump out facility in the harbour.

The bottom of the black water tank is approx 18" above the waterline on the Beneteau O38.

For cleaning, the manual states:

2) Use of toilets
- Every time the toilets are used, flush afterwards with copious amounts of water in the bowl using the toilet pump (manual or electric).
- When you are leaving the boat for several days, flush with fresh water, using for example the head's shower. Sea water that stagnates in the bowl gives off bad smells.

3) Maintenance of black water tank
- The risk of unpleasant odours forming increases when the waste water remains in the tank for a long time.
- Whenever possible empty the tank regularly even before it is full.
- Every time the tank is emptied put in about 5 litres of fresh water and add an appropriate detergent additive (available
from chandleries). A very simple method is soda salts, which clean and disinfect at the same time.
- Before winterising, flush the tank with copious amounts of fresh water filling it through the 'WASTE' deck connection.
Leave at least 5 litres of fresh water mixed with a detergent additive.
- Disinfecting: Disinfect the tank once a year by filling it with a solution of Javel water (1 to 1000).

I put "Javel water" on our Tesco shopping list. Confused the missus.

 

[ylop]

There are times, such as when berthed in Salcombe on buoy or anchor, when it is desirable to use the tank for solid waste for a few days, and the ability to shed urine directly (along with all the swimmers and fish) is useful.

Pee off the side and it will keep the swimmers away too!

 

[Fr J Hackett]

Then you should know to try an experiment before dismissing its empirical results! I’m suggesting to the OP that I had similar issues which due to bends in the paperwork I failed to mechanically rod, but I solved with the one acid I could buy in a remote location in large quantities cheaply. I was surprised how effective it was which is what lead to my hypothesis that the gas was having some effect.

Indeed, had I been close to a big town with trade suppliers I would probably have gone their first. But I was in the middle of nowhere with just a small corner shop.

Not in the UK. If you were lucky then one of the huge 24h ones MIGHT have it.

Of course, but if you’ve actually encountered the problem and checked out with many others who have then you’ll discover that sheets of crystalline material form on the inside of the tank then fall off. You don’t need to dissolve all that you need to break it up so the pieces are small enough to fit out the pipework. It could be shit and paper but you’ll find people who don’t use paper, or have been reliable using their system for years when they get a problem and those brave enough to get the marigolds out often find chunks of crystalline stuff.

Which is unlikely to be attacked by vinegar or hydrochloric acid. as you infer mechanical intervention by one means or another is most often the answer.

 

[Fr J Hackett]

Pee off the side and it will keep the swimmers away too!

Might frighten the horses as well.

 

[Graham376]

Just don't do what a friend did on his Bav. To clear blockages, he used to block the vent and then pump until blockage cleared. Last time he did it, the (full) tank split, took several months for the smell to clear.

 

[Mistroma]

Then you should know to try an experiment before dismissing its empirical results! I’m suggesting to the OP that I had similar issues which due to bends in the paperwork I failed to mechanically rod, but I solved with the one acid I could buy in a remote location in large quantities cheaply. I was surprised how effective it was which is what lead to my hypothesis that the gas was having some effect.

Indeed, had I been close to a big town with trade suppliers I would probably have gone their first. But I was in the middle of nowhere with just a small corner shop.

Not in the UK. If you were lucky then one of the huge 24h ones MIGHT have it.

Of course, but if you’ve actually encountered the problem and checked out with many others who have then you’ll discover that sheets of crystalline material form on the inside of the tank then fall off. You don’t need to dissolve all that you need to break it up so the pieces are small enough to fit out the pipework. It could be shit and paper but you’ll find people who don’t use paper, or have been reliable using their system for years when they get a problem and those brave enough to get the marigolds out often find chunks of crystalline stuff.

Not saying it wouldn't work, just take longer and indicating that hydrochloric acid would be more effective.

As for empirical evidence. I failed to see any for the "fizz" having an effect. That seemed to just be a guess on your part and I concluded it wasn't likely to have any significant effect. However, I am willing to revise that opinion if you propose a viable mechanism for the effect.

 

[johnalison]

Pee off the side and it will keep the swimmers away too!

There is nothing like the sight of a sheet of loo paper floating past to confirm my belief that I have no reason to want to swim in the sea.

 

[wingcommander]

Fill full of cola , drop in a few mentos mints , block vents , problem solved or something of a disaster

 

[ylop]

Not saying it wouldn't work, just take longer and indicating that hydrochloric acid would be more effective.

I am certainly not going to dispute that. I have no idea how long it took to work I added the Coke, sealed the boat up and came back expected to have to go find a pump out station and do some very horrible work and it was resolved!

However, I am willing to revise that opinion if you propose a viable mechanism for the effect.

I think there are two possible mechanisms: 1. pouring it down the pump out tube means you get a lot of fizz in the pipework right at the bottom of the tank which agitates any blockage (a gentle gas based plunging if you like) and improves mixing/agitates solids which make it easier to get the acids where you want it - you can likely achieve the same effect with a bit of wire. 2. We put it in and sealed it up the top of the tank which would have a similar effect to those who say to connect the dinghy pump to try and blow the blockage through. Now if the solids are Calcium carbonate then any acids will liberate CO2 and might achieve the same effect - but possibly a much slower rate of liberation as it’s got a limited surface area.

After the blockage was cleared there was quite a lot of this crystalline solid left at the bottom of the tank - I scooped out what I could and flushed the rest through. I genuinely hope never to repeat the process (it was probably 20 yrs of gradual build up). 2x 50p bottle of cheap coke may make it to my pre-winter layup procedure.

 

[samfieldhouse]

Well thank you all for your replies.
It would appear the tank has no tube extending down from the sucking point, so needed a LOT of vacuum to empty. I taped up the breather and that seemed to help.
Tested by filling it clean, and with the seacock open it drained nicely.
I’ve suggested a no paper rule!
Thank you all.
I can see there’s some coke fuelled debate, but I do want to thank everyone for your insights, much appreciated!

 

[Mistroma]

I am certainly not going to dispute that. I have no idea how long it took to work I added the Coke, sealed the boat up and came back expected to have to go find a pump out station and do some very horrible work and it was resolved!

I think there are two possible mechanisms: 1. pouring it down the pump out tube means you get a lot of fizz in the pipework right at the bottom of the tank which agitates any blockage (a gentle gas based plunging if you like) and improves mixing/agitates solids which make it easier to get the acids where you want it - you can likely achieve the same effect with a bit of wire. 2. We put it in and sealed it up the top of the tank which would have a similar effect to those who say to connect the dinghy pump to try and blow the blockage through. Now if the solids are Calcium carbonate then any acids will liberate CO2 and might achieve the same effect - but possibly a much slower rate of liberation as it’s got a limited surface area.

After the blockage was cleared there was quite a lot of this crystalline solid left at the bottom of the tank - I scooped out what I could and flushed the rest through. I genuinely hope never to repeat the process (it was probably 20 yrs of gradual build up). 2x 50p bottle of cheap coke may make it to my pre-winter layup procedure.

Busy but productive day in 34C temp. Winch motor in for repair, shopping done and some Winches serviced. So quite tired.

Still dubious about the fizz. Initial pour would lose a fair bit of gas. However, the reaction rate would be so slow that not much would have happened. I doubt pressurising would be significant either and would actually slow further gas evolution, minimising any stirring effect.

I thought you might go down another route involving carbonic acid or nucleation, etc.

I'm afraid we'll just have to differ on this. Even neat coke would only have a pH around 2.5-3 and reaction rate would be pretty slow. The actual amount of Calcium Carbonate removed with 3 litres of Coke would be very small. If Coke is 0.25-0.3% Phosphoric then you probably dissolved under 5gms carbonate. To be fair, it would probably be hydrated and could be 8-10gms crystals. This reaction would be very slow.

I wonder if agitation might even be counter productive. Allowing the phosphoric acid to slowly seep into the blockage could allow it to find weak points on the lattice structure and cause fragmentation. I vaguely remember a paper about that effect but not in this context (even remotely). That would allow removal of a tiny amount to cause catastrophic collapse of the crystal structure.

I believe you rectified the problem with around 3 litres of Coke and imagine the blockage was larger than 10gm. Something caused the collapse of the blockage. As I've said we can disagree about significant impact of the existing CO2 in Coke.

I might do some detailed calculations tomorrow out of curiosity. I worked out how much HCl was needed to dissolve material in a fully blocked pipe. The amount per metre was huge. Even HCl is mainly useful to regularly remove thin layers in pipes.

 

[KompetentKrew]

I haven't read all the replies but my holding tank is similar, except that it lacks proper pump out access at the top and when it was clogged I had to empty it with a jiggle syphon and a bucket.

I'm convinced that today's toilet paper presents no risk of clogging. Take some handfuls of toilet paper and dunk it in a mug of water to try for yourself - it just falls apart completely. My suspicions were confirmed when I performed this syphoning, as very tiny pieces of toilet paper were evident - it had been broken down into pieces maybe 2mm on a side.

I had use my gloved hand to clear the clog and it turned out to be a piece of calcium about the size of an old 50p, bound in place with shit. I'm convinced that pieces of calcium are the biggest risk to clogging.