Holding tank vent pipe

Resolution said:
OK so this is a touchy subject for me. We have a single holding tank down at seat level, with a long vent pipe up to an outlet just under the toe rail. Probably about 40mm diameter. Last season, chasing a bit of unusual sniff, I noticed that the holding tank was bulging under internal pressure. An emergency trip offshore enabled us to blow the tank and release the pressure. Diagnosis is that we had overfilled the tank sometime and the vent pipe had become blocked, dried out in the heat and is now cement strong. None of our efforts to flush the blockage back down have been successful, it is of course located behind some fixed joinery, so will require major works to remove and clear. This is on the agenda for next month, what joy :disgust:.
Morals of the sad story: don't overfill, and fit the biggest size of pipe possible.
Peter
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Maybe you need to replicate my non contact sensor system that sticks to the outside of the tank to warn you when its almost full https://youtu.be/N7vgpBImEVs

TudorSailor
 
robertager1962 said:
Oh dear. Have you tried backfilling the vent pipe with water and leave to soak first and then use a flexible steel drain rod? Thanks for your feedback though.
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We have spent ages pressure squirting water at the outside of the vent, to no effect. The vent itself is a cast metal fitting which involves two right angle bends. This may prevent to unwanted incursion of sea water in normal circumstances, but it certainly stops the flexible steel rods which we have also tried.
tudorsailor said:
Maybe you need to replicate my non contact sensor system that sticks to the outside of the tank to warn you when its almost full https://youtu.be/N7vgpBImEVs
TudorSailor
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I feel so stupid about this. We have a three float system that tells you how full the tank is, we must have just kept on a bit too far when the red light came on. (One of life's really nice tasks is taking the floats apart every couple of years and cleaning the scale / crud off them. Yuk!!)

Anyway, next month before hauling her out for antifouling and other service stuff we will have a very thorough flush through of the tank, and then make a determined effort to dismantle furniture and get the bloody hose off. Wish us luck!
Peter
 
Resolution said:
We have spent ages pressure squirting water at the outside of the vent, to no effect. The vent itself is a cast metal fitting which involves two right angle bends. This may prevent to unwanted incursion of sea water in normal circumstances, but it certainly stops the flexible steel rods which we have also tried.

I feel so stupid about this. We have a three float system that tells you how full the tank is, we must have just kept on a bit too far when the red light came on. (One of life's really nice tasks is taking the floats apart every couple of years and cleaning the scale / crud off them. Yuk!!)

Anyway, next month before hauling her out for antifouling and other service stuff we will have a very thorough flush through of the tank, and then make a determined effort to dismantle furniture and get the bloody hose off. Wish us luck!
Peter
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Water alone is unlikely to do much. You might do better with something more aggressive. Caustic soda is traditionally used to clear drains but if this is difficult to purchase I suspect that hydrochloric acid might do the trick. Sold in supermarkets throughout the Mediterranean. Very low risk that it will damage any of the materials in use but a good flush through later is well worthwhile.

Caustic soda available on Ebay very cheap, specifically for unblocking drains.
 
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vyv_cox said:
Water alone is unlikely to do much. You might do better with something more aggressive. Caustic soda is traditionally used to clear drains but if this is difficult to purchase I suspect that hydrochloric acid might do the trick. Sold in supermarkets throughout the Mediterranean. Very low risk that it will damage any of the materials in use but a good flush through later is well worthwhile.

Caustic soda available on Ebay very cheap, specifically for unblocking drains.
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Available from B&Q and probably other DIY and hardware stores

https://www.diy.com/departments/b-q-external-caustic-soda/36329_BQ.prd

BUT be very careful with caustic soda. Avoid all contact and risk of splashing on exposed skin especially eyes. Permanent damage is likely if splashed into the eyes as well as being excruciating painful
 
macd said:
I think Resolution, the person with the problem, is in Turkey, so B&Q won't be much help. Nor to many others on this forum. However, caustic-based drain cleaners are available in most countries, although you might need Google translate when you go shopping.
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Buying a face shield and the other appropriate protective clothing could be a bit of challenge.
 
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VicS said:
Buying a face shield and the other appropriate protective clothing could be a bit of challenge.
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Why? I cannot speak for Turkey, although my experience of that country is that they are very safety conscious. Here in Greece we have several chandleries locally where they stock a lot more safety gear than the average one in UK.
 
VicS said:
Available from B&Q and probably other DIY and hardware stores

https://www.diy.com/departments/b-q-external-caustic-soda/36329_BQ.prd

BUT be very careful with caustic soda. Avoid all contact and risk of splashing on exposed skin especially eyes. Permanent damage is likely if splashed into the eyes as well as being excruciating painful
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Thanks for the warning! We have just spent another lump of my pension on having the hull repainted, so goodbye to faded mottled blue, hallo to Really Smart. I don't want to let any acid near the new paint!!
Very grateful for all the comments.
Peter
 
Resolution said:
Thanks for the warning! We have just spent another lump of my pension on having the hull repainted, so goodbye to faded mottled blue, hallo to Really Smart. I don't want to let any acid near the new paint!!
Very grateful for all the comments.
Peter
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Dilute acid may not be too bad but caustic soda is a very effective paint stripper ... although 2 pack polyurethane is probably resistant to it.
 
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