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jobrantley 03-22-2010 10:07 AM

Holding Tank Leaking into Bilge
Hi all,
I fear I might have a hole/leak somewhere in my holding tank. Can someone
please explain to me if it is standard to have an overfill valve/drain on all holding tanks and where it is normally located ,and where it would drain to if the tank was over filled? I don't have a great understanding of the holding tank system on my boat so please forgive if there are obvious answers to my questions. The holding tank appears to be fiberglass and is located in the starboard locker in the cockpit.
I think this is a case of me overfilling the holding tank. I have found the area
where I believe the tank is leaking into the bilge. It is on the starboard wall of my engine compartment with the holding tank being on the other side of this wall. There appears to be an approx dime size hole there that looks to be perfectly round (like it was placed there and not a crack or explosion) When I pump the toilet ( I have not been able to pump out the head
yet) I get a slow steady trickle out of this area. It doesn't leak out of this hole unless I am pumping the toilet. I haven't had a chance to fully explore this "hole" just yet as it is in a spot that is tricky to see. Could I have
exploded/cracked my holding tank or is this the over fill valve? The holding
tank also appears to have leaked back into the locker behind the head when the boat heeled over approx 15-20 degrees.
Thank you in advance for your help.


mitiempo 03-22-2010 10:20 AM

There is not an overflow on a holding tank for pretty obvious reasons.:eek:
There should be the inlet from the herad, the outlet(s) and one or 2 vents. Usually these are all on top but sometimes a pumpout is on the bottom. It sounds like you have a crack or other leak that has to be fixed. Best to get it pumped out and remove it for repair or replacement asap.

eherlihy 03-22-2010 10:33 AM

If you are lucky, this round "hole" is where the connection is made for the holding tank vent. Again, if you are very lucky, there may be a barbed fitting around this "hole" and all that you need to do is find the vent hose, and reconnect it to the barb.

The more likely scenario is that you broke the barb for the vent fitting off of your holding tank. The other scenario is that you have cracked the tank.

Here is a diagram (thanks to West Marine) of what the holding tank plumbing should look like;
I believe that your "hole" is at, or near, 5 in the diagram.

Go here to see the whole article.

mitiempo 03-22-2010 11:59 AM

eherlihy showed one possible arrangement. But in common with all there is no "overflow" outlet. It's possible you blew the vent fitting off the tank, possibly because the vent may be plugged. You should have a way of telling when the tank is 3/4 full - it's an ABYC regulation. If the vent was plugged and you filled the tank the pressure had to go somewhere. Hopefully you have access to replace the vent fitting but you should get the tank pumped out first. If you don't have access removal of the tank is necessary to repair it. Good luck.

sailingdog 03-22-2010 12:37 PM

If you overfilled the holding tank, there is a good chance that you have clogged the vent line. In that case, when you fill the tank, it will become pressurized, and there is a very good chance that it will leak.

chef2sail 03-22-2010 04:39 PM

HOw do you clear clogged vent lines?

mitiempo 03-22-2010 07:06 PM

Remove and bend the hose to break up whatever :eek: is clogging it and run water through it. If that doesn't work bang the hose on the dock a few times to loosen the blockage. Or replace it.

jobrantley 03-22-2010 08:17 PM

Thank you guys for your explanations and diagrams...very helpful. I hope that it is just a clogged vent line. I believe it is a pretty stout fiberglass tank so it would have to be a lot of pressure to crack it. I am pumping it out ASAP and will do a much more in depth inspection then.
Thank you again for everybodies help.


sailingdog 03-22-2010 09:01 PM

If you have access to the vent fitting, you can often backflush them with water to clear them. You really should do this at least every time you pump out the holding tank.


Originally Posted by chef2sail (Post 583855)
HOw do you clear clogged vent lines?

CalebD 03-22-2010 09:30 PM

What steps have you taken to removing the offending liquids from your bilge so far?
If you have already broken out the bleach and ammonia so be it but I would recommend using the Raritan tank treatment 'KO' in your bilge with some fresh water to help reduce the offending substances to something a bit less offensive. 'KO' is a bacterial product that works best by itself with no harsh chemicals like bleach, ammonia and other household cleaners. It can help to reduce the stench factor allowing you to actually clean (yes, by hand) the residual crap in your bilge.
A similar situation happened to me once. Since we re-installed a new holding tank I know where all the important lines are and how they work. It seems that many of us learn more from our mistakes then when things go right. I was motivated to fix our vent line problem because I hate the stink of rotting you-know-what in any boats cabin. Smelly holding tanks can ruin an otherwise gorgeous boat for me. That smell alone can make me want to swim for shore.
I recommend Peggy Hall's book on the subject of marine sanitation devices (MSDs).
Good luck fixing this and sleeping on the boat in the future.

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