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John_colpitts 08-31-2006 10:33 AM

Holding Tank Questions
We live in a part of the world (coastal Canada) where overboard discharge is legal, and in fact is the norm. We just bought a US boat on which the overboard discharge valve is seized shut, so if we are gonna use the head, apparently we are gonna use the holding tank. It's probably time to be start being a bit more environmentally sensitive anyway. We do have a pump that will allow us to pump the holding tank overboard, or we can pump out at the local facility. But, having zero experience with holding tanks, I have a couple of questions:

1) Do people add something to the holding tank to assist with the biological processes of decomposition? Or is this dependant on the length of time between pump-outs?

2) Our tank is only 15 gallons, how long is that likely to take the 2 of us to fill? (2 days, 2 weeks, ???) (I'm pretty proficient at using the urinal in the stern of the boat, the Admiral hasn't mastered that one yet:D )

3) The boat has been on the hard for 2 years, I would like to pump some mineral oil thru it to lube the seals, but I think I read somewhere that the oil is not good in the holding tank. Any advice on this?

4) What is the process at the pump-out facaility? Is it just a matter of sticking the pump hose in the deck fitting and sucking the contents out of the tank? (that is waaaay to easy...)



sailingdog 08-31-2006 10:47 AM

Well FWIW-

1) Depends on how well ventilated the tank is. A well-ventilated tank shouldn't need assistance, where a poorly ventilated tank often will. The bacteria that do most of the waste processing are highly aerobic, the ones that make the stuff stink to high heaven are anaerobic.

2) Depends on the type of head you have, how often it is used, and how you flush it.

3) I've never heard of mineral oil being destructive of the seals or parts in a holding tank. YMMV, but I don't think it is much of an issue. BTW, if anyone knows anything more definitive, please let me know.

4) The best thing to do, when you're going to be pumping out the tank is to fill the bowl of the head with freshwater and pump it dry, then repeat. Then as a final step, fill it a third time and then leave the lever in the pump dry position. This does two things. One, it flushes the system with fresh water, so the amount of sewage and salt water in the hoses is minimized. It also helps loosen and dilute the sludge in the holding tank. And finally, when you go to pump out the holding tank and attach the hose, you will know the tank is completely empty because it will empty the water from the bowl for you.

Hope this helps.

Cruisingdad 08-31-2006 11:04 AM

1) Yes, most people use an additive. There are so many products, I could not go through them all. West Marine actually has a nice write-up (in their catalog) on the pros and cons of each. I have used pretty much all of them with marginal results. The best one has probably been KO and CP, which is a biological treatment. However, it is expensive, has quirks (like you can only use CP to clean the toilet), and may have varying results on boats up north (temperature will slow bacterial growth).

I have recently plummed in a new system that uses a in-line strainer with cholorine and the blue teflon tabs (like you buy at walmart for home use). This keeps that awful smell from fumigating the boat when you pump the head, it is inexpensive, and so far seems to reduce the head smell to zero. ANother sailor I know has been using it for 15 years with no problems. Call the mfg of your hoses and tanks to make sure it is ok first. I did and it is fine.

2) 15 gallons. Manual head? You will be lucky to get by a week. Better put a tank minder on that thing if it does not have one now. First time you overfill into the vent hose, it will clog it and you will forever have a atrocious smell on your boat.

3) I cannot think of why the mineral oil will hurt. I do not know that it is neccessary???? Others may know better.

4) Yes. Once you have the prime, with the nozzle closed off, stick the hose into the pump out t-hull. Open the nozzle. It ususally has a sight glass that shows you when you have sucked air, but it also shows you water quality. Once you have pumped out, fill it with several gallons of water and repeat this process until you are pumping fairly clean water. THis gets a lot of the junk off the bottom and keeps a cleaner (and better smelling) tank. Then go below and add your favorite formula to your head and pump it through a bit.

hellosailor 08-31-2006 11:32 AM

Mineral oil will kill the good bacteria in the tank, don't use it.

"Cesspool" additives, enzymes to help decomposition, are a good idea. Way cheaper than the marine versions of the same stuff. But with good ventilation and keeping the toxins (bleach and oil) out of the tank, it should build up the right bacteria balance to keep itself in good shape. The tank MUST be well ventilated to work properly, and if you can run two vent lines to different places ("flow-through ventilation") that wil keep it odorless. One good vent line can do the same thing, just not quite as reliably.

If that valve really is seized and you can't free it up, just replace it, in the long run that's probably simpler & cheaper & faster.<G>

One thing that will help the tank is your choice of toilet paper. Some brands are made from finer softer pulp and they dissolve faster, and that's what you need. (Offhand, I think Charmin is one of them in the US.) If you take one sheet of toilet paper and place it in a bowl of water, and it dissolves on its own, that's good. If you come back and it is still a solid sheet--that's bad. Whatever meets your needs and dissolves fastest, that's best for a holding tank.

svindigo 08-31-2006 01:29 PM

If you pump oil into the holding tank the oil will end up on the surface of the contents in the tank and oxygen will not be able to get to them. If I recall correctly you need good aerobic bacterial activity to keep the holding tank happy. Oil will only allow anaerobic bacteria.

Hope this helps

hellosailor 08-31-2006 01:54 PM

Exactly. The anaerobic ones "breath" sulfur instead of oxygen and they make the "stink of low tide" form sulfur excretions. Same same in the holding tank.

If you have the luxury of adding a fresh water blivet near the head, and IF you can use fresh water to flush the head (and backflush the inlet hose) you'll also find there's much less stink. Decomposition of critters in the sea water also causes a lot of odor. If you can spare an extra fresh water source (a flex bladder is fine) to use rather than raw water to flush the head, all the better.

sailingdog 08-31-2006 02:12 PM

Cruisingdad- Those chlorine tablets may attack the seals and other parts of the head system, so you might want to be careful with them.

BTW, Peggy hall recommends vegetable oil, rather than mineral oil. Probably because the bacteria can digest it...and then it doesn't form a layer on top and block oxygen from getting to the water.

John_colpitts 08-31-2006 02:55 PM

Thanks for all the good info folks. It is HUGE help!


Cruisingdad 08-31-2006 03:34 PM


Regarding the cl tabs... I know. This is an experiment in process. I did call the mfg, they said it would be fine... but I am (like you) - skeptical. I would never have done it, but I have two other people in the marina doing it and have been for 15 years??

I will say one thing: that smell that seems to permeate boats is gone from mine. Within an hour my boat smelled BOAT SHOW NEW BABY!! HAHA!! <No, I am not kidding>

Course, I have this strange blue liquid leaking out of the head, the holding tanks, etc... but hey, it all goes in the bilge and dissapears? (I wrote that for Surf's benefit, whom I think has left the board). <Of course, I am just kidding here Surf>

Surfesq 08-31-2006 03:39 PM

I haven't left the Board, I just have to work once in a while. I have said my solution to the holding tank odor issue many times. After the pump out, fill the tank with fresh water then re-pump. Add some Clorox Bleach down the pumping line, following with a squirt of water. That eliminates the odor. But let's face it, when you have a box of **** in the bottom of your boat, It's pretty much gonna smell no matter what you do. That's just a fact.

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