Piddle in pipes... the chemistry please.

[vyv_cox]

As has already been stated NOT every one. There is no path for contaminated water to enter the inlet pipe on a Lavac, unless you count the possibility of contamination being drawn into the inlet from outside the boat. We still occasionally get the rotten egg smell on the first flush after the loo has stood idle for a week or two.

A brave statement that there is no path, although I accept that the design of the Lavac is not as I described above. What prevents contaminated water in the bowl from finding its way into the suction pipe?

 

[chrisbitz]

I know nothing about these things, but just as a question, why wouldn't a bottle of appropriate acid dissolve the salts?

Are salts alkaline, or base? I'd imagine there must be some chemical that you could leave in the pipe for 24 hours that would dissolve the deposits?

 

[pvb]

Toilets don't have to be badly serviced for contaminated water to return to the inlet pipe - every one does it. When the 'bowl empty' function is used the suction valve to the pump is held open and the discharge valve is held closed, with the result that contaminated water sloshes backwards and forwards along the suction pipe. Contamination of the pipe walls is inevitable.

Which toilet are you describing? Certainly not the common Jabsco - with that design, moving the lever to the "bowl empty" position opens the discharge valve, destroying the suction in the pump, so that seawater isn't sucked in. Water can't "slosh" backwards and forwards along the suction pipe, as the suction valve flap will stop it.

 

[charles_reed]

I'm no expert, and this is guesswork based on A-level chemistry and too much knowledge about urinary problems! Thsi page (http://en.wikipedia.org/wiki/Uric_acid) is informative.

Basically, Uric Acid is the final result of your body breaking proteins down, and is excreted in urine.
Uric acid is not very soluble, and is much less soluble in cold water than hot. It forms salts with sodium, calcium and potassium (which are all present in sea water), none of which are very soluble. Ammonium Urate is insoluble in cold water, and is a breakdown product of Uric acid under some conditions, especially the anaerobic conditions that might obtain in a plumbing hose.

So, what gets deposited is probably a mix of various salts of Uric acid.

The interesting thing is that this is the mechanism that causes bladder stones. However, bladder stones are a symptom of a) excess uric acid being produced and b) highly concentrated urine. So, my guess is that blockages in marine toilets caused by build up of uric acid scale can be avoided by ensuring that people are adequately hydrated - in other words, they pee pale yellow, not orange.

Gout is, of course, concentrations of uric acid in the joints. Those with little knowledge of chemistry might think that bleach down the sea-toilet would be a "good thing", unfortunately commercial bleach contains sodium hydroxide as a stabiliser and that increases the deposits which react well with strong acids (being carbonates of various kinds).
So those who control their loo-destiny use either hydrochoric (muriatic) acid, nitric or sulphuric acid, to make in fizzle and bubble. I, personally, use a slightly less aggressive acid, sulphamic acid, to clear away the worst of the deposit.
For toilets in continuous use it's still necessary to take the piping off and clear it out - I do it about once every 5 years when it's not too major a task.
Whilst everyone drinking 5 litres a day (mind it musn't all be wine or beer) might put cardiologists out of work - I don't think it would put paid to blocked sea-toilets.

 

[VicS]

I know nothing about these things, but just as a question, why wouldn't a bottle of appropriate acid dissolve the salts?

Are salts alkaline, or base? I'd imagine there must be some chemical that you could leave in the pipe for 24 hours that would dissolve the deposits?

Plenty of people do that. Occasionally flush through with some hydrochloric acid or even with distilled vinegar every time they leave the boat.

HCl has the advantage of being a strong acid and being available in fairly high concentrations . Quick acting but very corrosive.

Vinegar is a relatively dilute solution of a weak acid, acetic acid, so less dramatic in its action. Possibly not good for some seals but it does have some mild disinfecting properties

 

[alant]

I'm no expert, and this is guesswork based on A-level chemistry and too much knowledge about urinary problems! Thsi page (http://en.wikipedia.org/wiki/Uric_acid) is informative.

Basically, Uric Acid is the final result of your body breaking proteins down, and is excreted in urine.
Uric acid is not very soluble, and is much less soluble in cold water than hot. It forms salts with sodium, calcium and potassium (which are all present in sea water), none of which are very soluble. Ammonium Urate is insoluble in cold water, and is a breakdown product of Uric acid under some conditions, especially the anaerobic conditions that might obtain in a plumbing hose.

So, what gets deposited is probably a mix of various salts of Uric acid.

The interesting thing is that this is the mechanism that causes bladder stones. However, bladder stones are a symptom of a) excess uric acid being produced and b) highly concentrated urine. So, my guess is that blockages in marine toilets caused by build up of uric acid scale can be avoided by ensuring that people are adequately hydrated - in other words, they pee pale yellow, not orange.

All sodium & potassium salts are soluble in water!

Calcium & magnesium salts are the culprits.

 

[nigelmercier]

I think that when the smell is a "bad egg" smell it is due to stagnant conditions of the trapped water leading to anaerobic bacteria acting on sulphates in the water to produce hydrogen sulphide.
Having said that I have kept bottles of clean sea water in the laboratory for prolonged periods without any nasty odours developing so it's not something that automatically occurs in clean uncontaminated seawater.

I think the bacteria only multiply in the dark, could this be the reason? The inner walls of the pipe get a slime of bacteria on them, and no amount of pumping will remove all of it. A Milton tablet in the incoming filter cures it within minutes.

 

[alant]

What actually happens

is that bacterial action on nitrogenous compounds in urine produces ammonia.

the ammonia raises the pH

At the raised pH calcium and magnesium, previously in solution as bicarbonates, are deposited as insoluble carbonates.

Sea water has a high temporary hardness due to dissolved bicarbonates.

Exactly!

 

[alant]

Plenty of people do that. Occasionally flush through with some hydrochloric acid or even with distilled vinegar every time they leave the boat.

HCl has the advantage of being a strong acid and being available in fairly high concentrations . Quick acting but very corrosive.

Vinegar is a relatively dilute solution of a weak acid, acetic acid, so less dramatic in its action. Possibly not good for some seals but it does have some mild disinfecting properties

Easier to use some cheap 'cola' from the supermarket!

 

[vyv_cox]

Easier to use some cheap 'cola' from the supermarket!

The acid content of cola ia almost neglible. I have tried it, it doesn't work and it's a lot more expensive than HCl. Hydrochloric acid is readily available, e.g. B&Q

 

[VicS]

. Hydrochloric acid is readily available, e.g. B&Q

as brick, masonry or patio cleaners but not all contain hydrochloric acid and some of those that do are fairly dilute.

 

[AntarcticPilot]

All sodium & potassium salts are soluble in water!

Calcium & magnesium salts are the culprits.

I didn't say they weren't soluble - I said they weren't very soluble, and you can reach a saturated solution fairly easily.

 

[alahol2]

A brave statement that there is no path, although I accept that the design of the Lavac is not as I described above. What prevents contaminated water in the bowl from finding its way into the suction pipe?

The inlet pipe of the Lavac enters inside the rim of the bowl. The pump deals only with foul water not clean, the clean is drawn in by low pressure in the bowl when the waste is evacuated. I guess if one had a knockdown whilst 'using' the loo you may get some waste into the inlet. Equally I suppose if the loo is left un-pumped and fairly full one could get flow back. Neither situation has occurred on our boat.

 

[Leighb]

There is no path for contaminated water to enter the inlet pipe on a Lavac, unless you count the possibility of contamination being drawn into the inlet from outside the boat.

This is likely to happen with any type of toilet. If, as is usual, the inlet is ahead of the outlet then when moored in a marina and the tide is flowing from astern there is a strong possibility of pumping in your own effluent. If it is slack water your effluent will be "hanging around" for some time.

 

[john_morris_uk]

This is likely to happen with any type of toilet. If, as is usual, the inlet is ahead of the outlet then when moored in a marina and the tide is flowing from astern there is a strong possibility of pumping in your own effluent. If it is slack water your effluent will be "hanging around" for some time.

That's a very possible scenario and explanation.

The Jabsco (despite whatever position of the flush/dry valve) can easily get contaminated water into the inlet side. Perhaps not far up the pipe (if at all?) but its CONTAMINATED water that smells as Vic's experiment demonstrated. He also tried no light/light etc and all had the same result. The freshwater flush solution cures the problem but NOT for the reasons people usually think.

PS I don't ever remember having a problem with smells using a Lavac. However they have their faults including the price...

 

[silver-fox]

We have a Jabsco toilet.

My simple, but effective solution to the bad smell that occurs when you first use a toilet that has been left unused for an extended time is to put about a gallon of fresh water into the toilet and pump out before leaving the toilet. I don't know why it works, but it does. Its simple to do too, if you have a shower outlet in the heads as a source of fresh water.

Regarding the build up of salts, I have tried everything, including pretty strong acid left overnight bubbling away but in the end the solution has been pipe out, thrash it on the quayside and put it back - seems to last about 4 years. Last time, the inner diameter of the 38mm pipe was reduced to around 10mm - I was amazed it worked at all.

 

[NormanS]

I've never been aware of any bad smells from mine, but the inlet is both forward, AND ON THE OTHER SIDE of the boat. However, that contributes to the huge length of pipe involved, which brings its own problems.

 

[vyv_cox]

Which toilet are you describing? Certainly not the common Jabsco - with that design, moving the lever to the "bowl empty" position opens the discharge valve, destroying the suction in the pump, so that seawater isn't sucked in. Water can't "slosh" backwards and forwards along the suction pipe, as the suction valve flap will stop it.

You may well be correct, i have been looking at the exploded diagrams but they are not detailed enough. I'm pretty sure that my RM69 was as I have described. I don't have a manual Jabsco to check where I am now.

 

[KAL]

As has already been stated NOT every one. There is no path for contaminated water to enter the inlet pipe on a Lavac, unless you count the possibility of contamination being drawn into the inlet from outside the boat. We still occasionally get the rotten egg smell on the first flush after the loo has stood idle for a week or two.

Us too. Definitely H2S but not sure how it develops. Rather like VicS's theory. Makes sense. We tend to flush the Lavac with two or three times the necessary pumps to get rid of it and it's fine thereafter.

 

[VicS]

You may well be correct, i have been looking at the exploded diagrams but they are not detailed enough. I'm pretty sure that my RM69 was as I have described. I don't have a manual Jabsco to check where I am now.

doesn't the design of the pump itself lead to a possible route for cross contamination of flush with effluent. The two are only separated by the O ring seal on the main pump plunger and any wear of that or scoring of the bore will result in cross contamination.

Also if I understand PVB correctly, and follow the Jabsco diagram correctly the Flush/empty valve holds the outlet flap of the flushing section of pump open so as the pump is operated air will be drawn in and out of flush side the pump from the bowl. That is surely also a route by which contamination of the flush side could occur.