Why am I covered in effluent?

[Papawads]

Warning: if you're squeaming or eating, do not read on.

I have a simple black water tank in the front heads, which was blocked. Methods of unblocking, already has a good thread by someone, I just want to talk tank construction here.

Two large pipes in the bottom, one from toilet, one to sea (with valve) and a breather.

Having failed to unblock the fault, I resorted the draining the tank into the floor of the heads, by loosening the pipe from the toilet and removing the joker. Then using an electric pump to dump overboard. An HORRIFIC experience, but much much worse was to come.

Now (I assumed) my tank was empty, and the blockage was in the outlet pipe. I removed the seaward pipe from under the tank (looked ok). So I stuck a gloved finger up that tank outlet and sure enough there was hard solid matter.

Thinking there may be a little residual Liquid in the tank (having drained the other pipe) I put a small bucket underneath and poked a stick up to clear the blockage.

ABOUT 50 LITRES OF PURE BROWN GUSHED AT INCREDIBLE FORCE FROM THE OUTLET, with me literally covered in it and screaming for the admiral.

I cannot convey the next 4 hours and I'm drinking heavily now to recover.

My question. How come the joker-free inlet pipe was dripping dry, and the tank still contained 50 litres of the very worst, still under huge head of pressure?

The Admiral is as quiet as a benedictine monk, I think the price for today will be very very high. If could at least explain WHY, I have a toe hold into matrimonial recovery.

Papawads

[alctel]

I cannot really help, having a composting head (mostly cos of stories like this) but you have my deepest sympathies and I hope you have recovered sufficiently! That sounds so nasty.

I would imagine some kind of hydro/air lock somewhere

[wholybee]

The inlet from the head probably goes up a pipe inside the tank. Ideally it would go nearly to the top, so that there isn't any chance of the tank emptying through the head when the joker valve wears out or gets clogged.

A "safer" way to service this would be to open the through hull, and run a pluming snake from outside into the tank to break up the blockage. Offshore, of course.

[PNWSalmon]

It sounds like your tank air vent may be blocked and your tank became pressurized. Make sure the air vent is totally clear. There may also have been calcification and a blockage that you poked through just enough for the pressure that had built up to do the rest. This is a traumatic experience for sure, but it seems that every cruiser goes through this as some point.

[Statistical]

Originally Posted by PNWSalmon

It sounds like your tank air vent may be blocked and your tank became pressurized. Make sure the air vent is totally clear. There may also have been calcification and a blockage that you poked through just enough for the pressure that had built up to do the rest. This is a traumatic experience for sure, but it seems that every cruiser goes through this as some point.

This. With each flush there was nowhere for the air to go so the air in the tank just kept getting more and more compressed. Like filling a balloon with a mixture of sewage and compressed air. When the OP poked the outlet with a stick well now there was a place for that high pressure mixture of sewage and air to go.

Anytime the vent gets blocked you can still flush the toilet it will just be a little bit harder and the next flush a little bit harder. I don't think blocked vents are common enough of a problem to warrant it but having a pressure gauge on blackwater tank would show rising pressure with each flush as the poop-air bomb is slowly armed.

[SV_FlyingTigress]

Had the same experience with my RV, except the black water pipe snapped clean off at the holding tank when I depressed the plunger guillotine valve too quickly after the hose came out of the ground receptacle. Got a 4" gusher right in the chest and upper body. Ran around to the other side of the coach to get to the wash hose (followed by a growing cloud of flys). Stripped right there in the RV park and hose showered off. YUCK!! Surfs up! Was a really "special" experience.

[PNWSalmon]

Originally Posted by Statistical

I don't think blocked vents are common enough of a problem but having a pressure gauge on blackwater tank would show rising pressure with each flush as the poop-air bomb is slowly armed.

Interesting idea on a pressure gauge, but probably too complicated. We now listen carefully when we open the holding tank, if there is a pop or loud hiss we go on alert for possible air vent blockage. There should be no sound. As the pressure inside and outside the tank should always be equalized if the vent is open/unblocked.

Just another part of the routine on the boat. And one we wish we knew before the unhappy incident.

[MicHughV]

Some time back I had an electrosan electric toilet unit. It was mounted under the forward v-berth.
For reasons still unknow today, one blissful night it exploded around midnight and sent it's contents in every direction.

Fortunately, there was no-one sleeping up there that night, as the force of the explosion blew the cushions and plywood underneath clean off.

To say that the entire v-berth was covered in s**t, would be the understatement of the year.

I think it took two days to clean and scrub the v-berth. In all my life, I can't think of a single more odious job I've ever had to do.

[mvweebles]

Originally Posted by Statistical

I don't think blocked vents are common enough of a problem but having a pressure gauge on blackwater tank would show rising pressure with each flush as the poop-air bomb is slowly armed.

Blocked air vent is fairly common. Many long time owners retrofit a much larger vent - perhaps 1-1/2". Also helps aerate the effluent which helps keep odor down. I went Compost due to nasty surprises like the OPs. Compost has other issues, but they are predictable. If I returned to traditional head system, would definitely install a large vent.

[Scubaseas]

Vent hose being clogged would account for the pressure.. Mud daubers LOVE to build nests in the vent fittings. I had one that built a large nest about 12" from the vent itself. Completely clogged the vent line and led the tank to be pressurized. Best to remove the deck pump out cap to release any pressure. If you have a fuel tank they can build a nest, you can run the engine for about 20 minutes then it quits running. Same issue. Clogged vent hose.

Then there are times when boats just suck.

[JPA Cate]

First, I am so sorry this has happened to you, and your good lady, Papawads. It may be the single worst thing that can happen inside a boat, to a boat owner, and I, also think it would have been a blocked vent line. The way forward is going to involve first of all, a deep cleaning, and sanitizing. You might consider a motel for a few days. It will probably be time for new cushions, and covers, when the time comes, and after all the underlying problems are solved.

In the future, I would make sure any vent lines have a fine screen cover, to keep out insects, if you stay with holding tanks. It is an opportunity to shift to a dessicating toilet, with which you don't have to deal with fermenting fecal matter at all. CF member Mike OReilly has written many posts about them, and a CF Custom Google Search should get you to some to read about if you want to go down that road.

Good luck with it all.

Ann

[peghall]

In the future, I would make sure any vent lines have a fine screen cover, to keep out insects, if you stay with holding tanks.

Unfortunately, Ann, Screens get clogged with dust and pollen and metal ones corrode, also creating a vent blockage. It may take a bit longer than it takes the typical "vent" thru-hull, but screens don't provide immunity from blocked tank vents.

However an open bulkhead fitting instead of any "vent" thru-hull can because it allow you put a hose nozzle against it to back flush the vent line every time you wash the boat and/or pump out...or, if you never wash the boat and always dump instead of pumping, you can still use a washdown pump--even sea water--to back flush the tank vent.

And while I have the floor for a moment... A a waste tank vent provides plenty of warning that it's becoming blocked. You start to find that you're encountering increasing resistance when you pump the toilet...electric toilets "burp," and start to backflow. Those are the first clues that your tank vent is becoming blocked...cease using the toilet NOW and open the pumpout cap to relieve any pressure before it builds up enough to turn the tank into "Old Faithful" when you finally decide to open the cap.
I've been there, btw...the boat was in its slip, I was aboard alone and not knowing the system could be pressurized...owner failed to mention that li'l detail...I opened the pumpout cap and I was downwind of it. I was over the side and into the water--deck shoes, watch, sunglasses and hat--before the spew was over! Fortunately unhurt and didn't lose anything I was wearing.


--Peggie

[Lepke]

I use to have a dairy. I spread the liquid cow poop with a large sprinkler the size of a small cannon that makes a 100' circle. We called it the big gun, it's on wheels and made from 3" aluminum pipe with a nozzle necked down to 1". It was connected to my pump with sections of aluminum pipe. I was spreading downhill from my barn when it stopped spreading. I stopped the pump and walked down the pipeline with a hired hand. Sprinkler pipe has a rubber seal between sections. As pressure builds there will be little leaks until about 10psi. And when you shut it down as the pressure drops the leaks come back until the pipe is empty. What I didn't count on was the downhill. There was about a 20' head.

As we walked along the pipe, the first sections were leaking at their connections, so I assumed there was no pressure. The nozzle was plugged with a small piece of wood. I can still remember the sight of the nozzle and plug some 35 years later. Facing the nozzle I turned it a 1/4 turn to release it and my world turned green. I had cow poop slurry everywhere. Little particles in my eyebrows, mustache, hair, you name it. And my hired hand didn't get away clean either. He was laughing so hard he slipped and fell into the stuff we just spread.
Anybody that spent much time around cows has many cow poop stories.
Not me in the pic. But I looked much worse.

[Shanachie]

There are many ways a vent hose can clog.



One is that some/many boats have 3/4-inch elbow fittings where the hose meets the hull. These are easy to clog and a bear to clean because you usually can't run a "snake" through them.


It's particularly bad if you accidentally overfill the holding tank while at a marina with a broken pump-out system. (Garrison Bight in Key West a couple of years ago.)


I managed to clean the elbow fitting with 18-inch cable ties. Jam one in from the outside, twist it around and pull it out. Then jam about five of them in, one at a time, and twist them as you pull them out.


I figured that out after opening the pump-out cap and getting a foot-high geyser. It probably would have been better to be a jerk and just macerate into the harbor.

[wholybee]

While everything about vent hoses in this thread is true, the vent hose is not what caused the 50 liters of waste to flood the boat. Read the first post carefully. The OP had just "emptied" the tank through the hose to the head. A clogged vent might cause it to "glug glug" while emptying through a hole in the bottom of the tank, but would not prevent it. Likewise, the once the solid blockage was removed from the main tank drain the waste emptied readily from the bottom of the tank, just as it should. Only he thought the tank was empty at that time.

With that said, once in this mess, absolutely check, clean, and replace, refurb the vent hose. But I think the issue here was that the OP thought he could drain the tank through the hose to the head and didn't realize that hose probably goes to the top of the tank internally.