Decomisioning Holding tank question

[Alan Wheeler]

OK so who here thinks this is just plain and simple a bad idea. I have a 1000'ish ltr water tank">fresh water tank built integral to the hull. I also have a tank close to twice that size that is also part of thehull. This bigger tank is my holding tank. The problem is, there seems to be an air leak somwhere. When we sail or get into ruff water, the stink below becomes so bad we can't go down there. I have tried everything I can think of. So I am now at the point of maybe decomissioning the tank and building a new one and one that is much smaller.
Here's the question, do you think it is possible to clean this old tank enough with doeses of chlorine and doses of hydrogen peroxide that this tank could eventually be turned into another fresh water tank?? Now when I mean fresh water, this is for showering etc only. We take on our drinking water seperatly. Our fresh should be safe where we do fill up, but a ot of it comes from streams and I simply don't want to take a risk drinking it.
Thoughts??

Possible? Yes. Desireable? No way. Consider cleaning it out the way you have planned, and install a bladder inside the tank if you really want to use the space.

[dana-tenacity]

Assuming you could work it, you must never tell anybody.

[mike d.]

alan as some one who ran a pump out boat i would say ?i don't know. the only thing you can do is try it and see what happens. if you have an inspection port i would use high pressure and really good deoderizer detergent. mutiple times. if we had/have bad odorsin box trailers and or box trucks we buy a can of ground coffee and sprinkel it on the floor and leave it there. 1)it takes over the smell 2)it eventually eliminates the odor there is something about the acid in coffee grounds(fresh) that kill others. other than that i think i would get prof. advise. regards mike

I used to work for a septic pumping company, I have seen how far they can disinfect tanks. I have no doubt that it cold be done, but a bladder would be so much safer, and easier for people to swallow

[Pura Vida]

I'm with Kai, yes is might be cleaned, but there is no way whatever goes into that tank could be anything other than ballast in my mind. I can't sail for any time at all without getting scrapes or cuts that I would not want to wash with a risk of infection. What is keeping you from simply fixing it and returning it to waste water duty? It could sure save on replumbing.

[Alan Wheeler]

Yeah OK I hear ya all.
Why can't I fix it?? Well I have tired everything I can think of externaly. But obviously the leak/s are somewhere I can not get at. The tank spans the entire hull and half is under the Galley. There is no way of getting at that part without ripping out the galley and that would mean a total rebuild which I ain't doin. The tank is also devided in two with a large baffle, so I can not get at the side under the Galley. If I could, I would have considered a thorough cleaning and a good coating of some paint on membrane. All the plumbing is connected to that hidden half of the tank as well. So getting a bladder in there is also impossible. This tank effectively divides the bilge areas in two seperate sections. This is a large empty bilge area infron and one behind. Plumbing enters the tank both sides. There is good access to both sides. So I thought I could put two new smaller holding tanks each side so as the plumbing could be connected.
I most likely will still go with the new tanks idea, but I just wondered about what to do with this space. Of course, filling the tank to the top with water may then mean I have water leaking from it into the bilge.
I suspect the tank has never been plastered correctly in the very beginning and I have a few small hairline cracks somewhere. The gas weeps through, but you only need a weep of that stuff to drive you out of the boat.

Have you checked the condition of the tank vent? And the vent line?

[delmarrey]

Originally Posted by Kai Nui

Have you checked the condition of the tank vent? And the vent line?

My first impression!
Are you sure it's leaking? Is there sewage in the bilge. One thing you can do to find a leak is fill it with a floresent dye then take'r out. Then with a black light shine it all around the tank where you can see and into the bilge. You should at least be able to find the general area where it's coming from.

Welcome back........................_/)

[Alan Wheeler]

Oh I have done everything you can imagine. Bilge is dry and clean. Tank vents? don't get me started on tank vents. I have tried every senario you can imagine. As for the tale of getting plenty of air into the tank to reduce odours, I can totaly gaurantte it has no affect what so ever. I currently have two tank vents. A 19mm 3/4" and a 32mm 1 1/4" hose. I have now made it so air actually circulates through one and out the other hopefully creating a negative pressure in the tank. But nup, didn't work.
Oh and Del, this problem stops compleatly as soon as the boat is at rest. It is definatly gas, not liquid. And I think when I have sails up it is at the worst because I guess we have a such a lot of low air pressure around the boat due to the sail. so it must suck the gas out.
This has been a problem for three years. I have tried everything and it has cost a fortune. I even painted a tar based product over all the tank that I could get to. I think I cover most of it. I poured Epoxy and tar based sealants over the lid area's I could not get to. I have replaced all hoses. I have sealed and resealed all PVC joints. I have even gone over the outside of the joint with sealant. Every bolt and screw in tank tops I can find has been sealed so deep I am not sure I am ever going to be able to get the lid off if I ever have to.

[Charlie]

Wheels:

Two ideas don't know the value of them but I will throw them out.

1) Plug the vent holes and fill the tank with smoke. This may help you ID the leak.

2) There is an enzyme that is used in setic systems. It is supposed to be real good at eating all the waste. Clean the tank as well as you can and then add the enzyme. If yu want I can get the name of the product from my plumber friend.

[Boracay]

Since the politicians seem to have decided that one of the solutions to Australia's water crisis is to recycle sewerage into drinking water I would expect there should be no problem with emptying the tank, flushing it as best you can, disinfecting and then filling with fresh water. I could not advise following our politicians' lead and drinking the water but see no problem with showering.
Since you are going to use it for washing only my instinctive (no rational or scientific basis whatsoever) thought would be to put some sort of lime (calcium carbonate powder?) in the tank on the basis that the normal leakage would carry it into the micro cracks of the concrete.
My recollection of conversations with plumbers in my youth is that they did not mind working with sewerage, particularly when they came to make up the bill.
Your crew would probably find the attraction of a thousand litres of fresh water overcame any squeamishness.
There may be some risk to stability if you take a tonne from the bilge and (presumably) locate it elsewhere in the boat.

[Alan Wheeler]

thought would be to put some sort of lime (calcium carbonate powder?) in the tank on the basis that the normal leakage would carry it into the micro cracks of the concrete.

Thanks Chris. Actually it is not such a silly thought, I just don't know how practicle it would be for me to do. But even a good dose of cement poweder apparently can work. I just don't know how feasable it will be for me to do it and I was thinking I would then have a lot of cement gravitate toward the bottom of the tank.

[Chrisc]

Wheels,
I have exactly the same scenario on my boat - possibly not as bad as yours but then my sense of smell isn't up to much. With the boat on the berth, no problem. First day out sailing, pretty stinky, and then the smell either disappears or we get used to it. In my opinion, gas from the holding tank gets trapped in the hose from the toilet to the tank and when the boat starts leaping about the ocean, it percolates back up through the toilet bowl. Interestingly, if you apply the nose to the holding tank vent, it doesn't smell bad. Another source of really disagreeable odour is the salt water inlet pipe to the toilet. The first few pumps produces a sulferous smell that kind of puts you off your lunch.
Trying to find a solution to both problems at the moment.

Chris

[Alan Wheeler]

If you solve the smell of the saltwater going sulferouse, you'll be a rich man. I pour in some holding tank odour stuff into the bowl if I am away from the boat. That helps the water in the bowl. I gave up doseing the tank as it took $40 of product and made little difference anyway. Then you pumped it out. So that gets expensive.
I did wonder if the vent in the syphone break may have been a problem, but testing that didn't show any issue. I don't get any smell in the toilet area. It always comes from under the galley area.