Leaking holding tank?

[mcaswell]

In an effort to stop the source of odor in our boat, I replaced the hoses a while back, but the odor remains. I recently noticed a small pool of brown that can be seen under the bottom edge of the holding tank. Given that the location was on the side of the tank where all the fittings are, I suspected those fittings were leaking, though feeling along these fittings revealed no dampness.

So, I tried a different strategy... I cleaned up the stuff, and then put a folded up clean paper towel below the fittings (right above where the liquid was collecting). Checking back a few weeks later, the top of the paper towel was clear, but there was a new batch of liquid underneath.

Given that it appears that the leak is not coming from the fittings, I guess that leaves just the tank itself. The leak is apparently very slow... the "liquid" I observed is not free-flowing, but rather more like a small and thin area of damp brown goo, as if the leak is just barely keeping up with evaporation.

I guess my next step is to remove the tank to verify. If there is indeed a leak, is it something that I can repair with a glue of some sort, or do I just replace the tank? It's polyethylene.

--Michael

 

[Peggie Hall HeadMistress]

Replace is the only cure for a poly tank that's cracked at the bottom...

And it sounds like yours is. However, it may not be...the source of the brown goo may not even be the tank...you'd be amazed at the number of people I hear from who've replaced their entire sanitation system--hoses, tank, even the toilet--trying to get rid of what they thought was "head" odor, when all they really needed to do was clean--really CLEAN--their bilges or locate and remove some trapped water. We won't know for sure what you're dealing with till you get the tank out of the boat.

 

[mcaswell]

I do indeed need to give the bilge areas a thorough cleaning... my shower drain unfortunately is just a tube that leads to the cavity where the bilge pump is located, and water also collects in there whenever I pull out the speed transducer.

But the odor is especially strong when I open the compartment where the sanitation stuff is located... it's under a settee, and this compartment is not open to other areas.

--Michael

 

[Peggie Hall HeadMistress]

Step 1: Remove the tank...

I can think of several scenarios other than a cracked tank that could account for your odor...all of which will require pulling the tank out to cure the problem....so let's start with that and see what we're dealing with.

Warming the hoses will make it a LOT easier to remove 'em from the fittings. I'd use a blow dryer, not a heat gun...less likelihood of damaging the hose by overheating it.

Btw...what brand/type hose did you use when you replaced 'em? How long ago?

 

[mcaswell]

I replaced the hose with Trident 101, and it was about a year ago. Actually, thinking back to it now, I remember now that I observed the little blob of waste goo back then too, and was hoping that replacing the fittings would stop it.

Anyway, when the odor persisted, one thing I considered was that there was some leaked waste just sitting below the holding tank, occasionally migrating aft to the spot I would see it. So, I "flushed" the area underneath the tank very well, using a combination of water and CP, then sponged it up, and rinsed again.

--Michael

 

[mcaswell]

Peggy,

I have not yet had the chance to remove the tank, but I did go last night and take a closer look at the compartment, and there is something I think I might need to be concerned about.

The Ronco Plastics site mentions "The tank must be installed on a flat or contour matched surface, be clean and totally supported in all planes with 1/2" - 3/4" marine plywood or equivalent."

That doesn't appear to be the case for my tank's installation. Here's a cross-section of the tank:

Though I can't say with absolute certainly until the tank is removed, I'm pretty sure that due to the contour of the hull and settee, most of the tank's flat surfaces are not fully supported as Ronco dictates... how critical is this? I don't think it's practical for me to completely line the tank with 1/2" plywood, but perhaps I could add some blocking that would at least give it some support (more than it has now!).

I am going to try to get out there again soon to remove the tank, but due to time constraints, I might just have to order the replacement first with visually confirming that the tank is indeed cracked. But again, this compartment is not open to other areas... the only source for the foul-smelling brown goo that keeps showing up under the tank is the sanitation system, and there is no indication that it's the fittings, hose, or pump that are leaking, so hopefully that doesn't end up being a waste of money.

--Michael

 

[Peggie Hall HeadMistress]

Not that critical, Michael...

Especially not for a tank that small, and as sturdy as Ronco tanks are.

They make tanks for a number of boat builders and also for a number of industries other than marine...many of which are made to standards--wall thickness etc--specified by the customer...some of which are too thin to support the weight of the contents without support on all sides as well as the bottom. So they just include that "CYA" fine print that in the instructions for every tank they sell, whether it needs it or not. Support it on both ends and put a block under it in the middle...you'll be fine.

 

[mcaswell]

Great, thanks! I might be able to get out to the boat tomorrow morning to pull the tank. Otherwise, I'll just have to order a replacement and hope that's where the problem is.

The current tank has (surprisingly) a 3/4" vent line... should I take this opportunity to up it to 1", or is 3/4" sufficient?

--Michael

 

[Peggie Hall HeadMistress]

The bigger the better

So by all means up it to 1"...or even 1.5" if you don't think that's too big a hole in your boat.

 

[mcaswell]

Ronco didn't have a tank that would fit that area without a reduction of capacity (16, maybe 18 gallons vs. the current 20 gallons), and I need all the capacity I can get! So I got in touch with Duracast, who supplied the original tanks to Hunter, and ordered the exact size replacement from them.

One interesting thing... the vent fitting (hose is visible in the photo I posted) is on the side of my tank, but on the drawing they sent me, the vent fitting has been moved to the top of the tank, and near the bow end. I assume they moved it to the top so that it would be less likely to get clogged. They said they could put it anywhere I wanted, and I was going to have it be on the top, but at the aft end (a shorter run to the existing thru-hull), but then realized that they probably moved it to the front because I think the tank sits with the forward end slightly higher, so when it's close to being full, the vent fitting might still get clogged with waste.

It then occurred to me that perhaps Hunter relocated the vent thru-hull as well. So, I looked at some for sale listings of H310s a year or two newer than mine, and confirmed that the vent thru-hull was moved forward (I assume the vent hose routes forward through the v-berth locker, and the thru-hull is installed in there).

So, what I will do is install a new 3/4" or 1" thru-hull at this new location, connected to the forward vent opening on the tank as it comes, and also use the existing 3/4" thru-hull and hose attached to a new opening I'll add to the tank, to provide even better ventilation.

One last question... is it worthwhile to add a 4" deck plate for access to the inside of the tank for cleaning?

--Michael

 

[Steve Dion]

Michael: Did you check with Hunter to see who made those tanks for them? They may have a direct replacement if you are lucky. They can probably reposition the fittings too if that is what you want/need.

 

[mcaswell]

Yes, see my above post... Duracast made the tank originally, and I ordered a same-size replacement from them today.

--Michael