Can't pump out holding tank

[GiniL]

Of course. I don’t consider Saran Wrap as permanent for anything, including food!

[GrowleyMonster]

My money is on a leak at the top of the internal dip tube.

[Cadence]

Originally Posted by GiniL

Of course. I don’t consider Saran Wrap as permanent for anything, including food!

Duct tape would not let you see the point the Saran Wrap is being sucked in.

[CassidyNZ]

Originally Posted by GrowleyMonster

My money is on a leak at the top of the internal dip tube.

I agree. I never read all posts in total detail but I believe that the tube that brings the effluent up from the bottom of the tank the the suction Li e fitting us drawing air.

Even a smallish leak at the top of the internal tube will stop any suction from developing and the pump-out (actually an anomalous term) will fail.

Perhaps the solution to diagnosis is in the macerator pump line. In the picture it looks like the suction line for dockside pump-out is alongside the pipe running to your macerator. If this is so, is it possible that you can switch the pipes at the other end (away from the tank)? Because if the macerator is also drawing effluent up from the bottom in an internal pipe, the the deck suction line will work on the macerator connection.

Then, while drawing out the contents on the deck pump-out, you can check the vacuum on the original deck line. No (low) vacuum? Internal leak in the pipe.

Just musing, you may have already tried this.

[GiniL]

I was thinking of duct tape with the saran wrap only to hold the edges down so that the seal would be tight enough that air won't just pull underneath (if the issue is that the seal isn't good). But I'll try first with just saran wrap to see what happens . . .

Yes, the betting money should be on the dip tube itself or it's seal at the tank at his point!

Switching the macerator and discharge hoses and their connections to see what happens (or doesn't) is a great suggestion, just not workable here. The macerator hose is a short run to port. The deck discharge is a long run to starboard, so the only potential way to swap them is at the tank, where I can't get to them well enough. Plus, the hose material seems to be the stiff PVC stuff that almost always has to be cut off the connections (from all I've read) or ends up mangled once it comes off and has to be replaced. So I'm expecting that I'm going to end up with a repair involving the dip tube and/or seal into the tank, and a new deck discharge hose (which I'll have replaced with a much higher quality).

On going thanks for the benefit of the many ideas and suggestions you all have offered.

Gini

[Cadence]

Originally Posted by GiniL

I was thinking of duct tape with the saran wrap only to hold the edges down so that the seal would be tight enough that air won't just pull underneath (if the issue is that the seal isn't good). But I'll try first with just saran wrap to see what happens . . .

Yes, the betting money should be on the dip tube itself or it's seal at the tank at his point!

Switching the macerator and discharge hoses and their connections to see what happens (or doesn't) is a great suggestion, just not workable here. The macerator hose is a short run to port. The deck discharge is a long run to starboard, so the only potential way to swap them is at the tank, where I can't get to them well enough. Plus, the hose material seems to be the stiff PVC stuff that almost always has to be cut off the connections (from all I've read) or ends up mangled once it comes off and has to be replaced. So I'm expecting that I'm going to end up with a repair involving the dip tube and/or seal into the tank, and a new deck discharge hose (which I'll have replaced with a much higher quality).

On going thanks for the benefit of the many ideas and suggestions you all have offered.

Gini

Gini, please let us know the solution.

[jeepbluetj]

A vacuum leak should be reasonably easy to DX, if it's in the tank. Between the tank and the deck fitting I'm quite positive you could hear it unless the pump-out is really noisy.

So, are you sucking air or just pulling a partial vacuum?
1. Sucking air IN the tank, you can feel/hear air being sucked into the vent.
2. Sucking air outside the tank, saran wrap, ears, feel for it, smoke, etc....

Pulling a vacuum in the outlet line:
1. Very bad clog in the line or at the bottom of the dip tube. If you run water into the deck fitting it will fill up the hose, but not drain into the tank.
2. (longshot) multiple layer hose has delaminated so that the inside is "floppy" - so when you start to suck through that hose it collapses and closes up. This would let you drain from the deck fitting to the tank. (I've only actually seen this happen with fuel lines, not waste)
3. A piece of plastic or something (like the cutout from putting the fittings in the tank) that is acting like a valve - when you start to empty it gets sucked onto the bottom of the dip tube and closes it off. Or the dip tube was too long and is now against the bottom of the tank.

I'll bet a beer that you're going to have to pull that dip tube out. Boat Yoga is good for you.

[GiniL]

Boat yoga! Ok, that one had me laughing. I’ve been doing a lot of boat yoga on this issue. But little did I know it.

To Cadence: Yes, I will definitely give y’all a post-mortem. Once the problem and the cure and been chased down.

To jeepbluej: One slight challenge for me in working on this is that I do my boat mechanics and my many pump out excursions single-handed. I potentially can recruit someone to, for example, try to pump while I lay under decks and listen, watch cellphane, etc. But so far, the stubborn part of my nature has preferred to fuss with all this on my own time without imposing on anyone else. What I have noticed while doing my attempted pump outs is that I can’t feel much if any suction on the vent line when I am trying to pump out (the vent line opening is within easy reach of where the deck discharge fitting is located, so I can pump and check the vent at one time). What I can’t do is pump out while being in the bowels of the boat where the discharge hose enters the tank to listen, test for suction, etc. But I can wrap it in Saran Wrap and see what it does after an attempt to pump out, which I will do when I can get back to the boat for more work on this problem (sometime this week). I want to try one more pump out anyway since I did slightly tighten up the clamps on the deck discharge hose at the tank end. The slack I took out of them wasn’t enough for me to think that will change anything. But I’ll kick myself to the moon and back if tightening those solves the problem.

Instead, I agree: I think it’s either in the the dip tube or the seal around it. But I’m not going to be the one to pull the dip tube. I’m no shrinking violet, and I do “boat yoga” (now that I know that is what it is) better than many or even most. But I am older than many, light and small in stature, and as physical strength goes, well beyond my prime. I’m not too proud to say I’m not strong enough for some things. And I know I am not strong enough to get that discharge hose off (getting the vent hose off was challenge enough, and it ultimately required cutting).

I am about to schedule a haul-out for new bottom paint. The boatyard I’m using is well-capable of chasing this down once I have hit my stopping point. I’m pursuing it until then because I’m hopelessly stubborn, as well as hopelessly curious, and I like having my own sense of what the problem is before I turn to a professional to fix it. If nothing else, I’m learning a lot along the way. I thrive on that (for better or worse).

It may be several weeks, or a month or more, before I can report back with a final, authoritative report. The boatyard has to work me in. But I will report back, for sure. Threads like this are incredible resources for me, and I’m happy to do my part to add to the learning. So the thread may get a bit stale before I can close out my experience, but know that I will.

I remain grateful for everyone’s insights, advice, and encouragement. Thanks!

Gini

[GiniL]

I finally have a firm diagnosis: a “hole” in the discharge line a few feet below the deck and several feet away from the connection to the tank.

You may be wondering, first, how did I miss the hole? The answer is that the discharge hose is about 12 feet long. So it hard to get close to every inch of it to inspect (many things in boats are difficult to access, and the full length of the discharge hose is no exception). I finally got close to that area by pulling the refrigerator out, which gave me access to parts of the hose that were hard to view.

Next, you may be wondering, how the heck did a hole get in the hose? Especially given the fact that the boat is just now two years old, has been gently used (where the sanitation system is concerned), and the hose from all visible vantage points was as good as brand new.

The answer to that second question is: The hose was routed wrong. It ran closer than it should to the exhaust pipe for a forced air diesel heater. It took awhile, but after a lot of cold weather boating this and last December, with the heater running a lot, the hose finally melted through. Not a huge hole. Fairly small, as a matter of fact. I haven’t gotten back into the area well enough to actually measure it, but I’d say 1/4” to 3/8” at its widest (and irregular, as you might expect a melted opening to be}. It melted in a straight-down section of the discharge hose. Which made it harder to detect. I think that, when I ran hose water with high force and bucket water with low force down the deck discharge fitting, the water pretty much went right past that little hole and into the tank. Anything that went into the bilge area below drained right out without notice. Still, the hole created from the exhaust heat was big enough (obviously) to fully compromise any vacuum pumping effort.

Guess this is one for the record books. A one-off, I hope. Rare, if not unprecedented, and hopefully nothing anyone else will run into. But in case the solution to my mystery aids anyone reading this thread in the future, there you have it.

FWIW, I plan to get the discharge hose replace with a higher quality hose with superior flexibility so that it can be routed and secured well-away from that heater exhaust hose. Peace of mind not only for the integrity of the sanitation system, but for safety aboard more generally.

Thanks again, everyone, for your suggestions, thoughts and moral support. All’s well that ends well, and this one (happily) looks like it will end well (the dealership has gotten the manufacturer to agree to the repair, given the source of the issue).

Gini

[CassidyNZ]

I’m interested in how the hole in the discharge line didn’t result in bad odours in the boat. Maybe it was upstream of a carbon filter? Or something?

[GiniL]

Good question, but I don’t have a good answer. I didn’t have any bad odors.

My guess is that was because (a) my usage is light, with little to no solids and regularly treated with Raritan’s KO; (b) I tried to pump out right away after the three week or so period where I was using the holding tank somewhat regularly; and (c) after trying unsuccessfully to pump out, I left the boat sitting in the boathouse with the vent line open (after unclogging it) and with the cap off the deck discharge fitting to maximize ensure until I could get a transfer pump on it.

Maybe cold December weather helped too. Not sure.

[sailorboy1]

Originally Posted by GiniL

I finally have a firm diagnosis: a “hole” in the discharge line a few feet below the deck and several feet away from the connection to the tank.

Are you saying this hole was so big that it prevent being able to pump out the tank?

[dfelsent]

I imagine a quite small hole is all it would take to keep the pumpout pump from priming.

The line is under negative pressure when pumping. That’s how the waste is drawn up.

The waste pumps are not particularly high flow pumps, and a small air leak will leak more than the pump’s capacity.

Great find on the leak.

[GiniL]

Originally Posted by sailorboy1

Are you saying this hole was so big that it prevent being able to pump out the tank?

Dfelsent is correct — it takes only a small hole to compromise the vacuum and make it hard or impossible to pump out. This hole is between about 1/4 and 1/2 inch wide (or 6 and 12mm) where the heater exhaust actually burned all the way through the side wall (a larger area of about 2 inches in diameter is charred).

[dfelsent]

I will say the charring of anything from the exhaust would make me want to insulate and screen it big time.