Falling foul: how to unblock the boat's waste holding tank

Falling foul: how to unblock the boat's waste holding tank

Every year, people ask us how to deal with a clogged black water tank on their boat. So we've written an article on how to tackle this rather unsavoury problem.

When returning our boat, the charter company technician informed me that the waste holding tank was blocked on our Sun Odyssey 43 DS yacht and that it would cost me 150 Euros to unclog it. I was a bit annoyed because unblocking a clogged black water tank is a 5-minute job. Of course, it's never a good idea to do this job in the marina or at least not in the daytime. But I told the technician that I would sort it out myself and it was a simple job. So, from my experience, I can tell you exactly how to do it.

How does the boat's waste holding tank get clogged?

Black water tanks clog regularly on older vessels. No toilet paper is allowed down a marine toilet and even though you may tell the crew this several times a day, occasionally someone will throw some paper in. The best way is to answer the call of nature in the sea. Take a leisurely swim far out to sea, fully relax as you do, and then casually relieve yourself. The bidet is all around you, so there's no need for toilet paper. Then swim back to the boat just as relaxed.

YACHTING.COM TIP: Did you know that a clogged toilet is one of the most common reasons for the boat charter company to take your security deposit? Find out what others are in our article — The most common reasons for losing your boat rental deposit. The truth is that taking out deposit insurance will save your nerves and a lot of money, not just in the case of a clogged holding tank. So, what are the other benefits of getting coverage? Check out our 5 reasons to take out deposit insurance.

How to unclog a clogged toilet?

But back to the unclogging of the holding tank. So how do we do it? You need to grab a hose, get in the dinghy and paddle to the side of the boat to the pipe through which the tank leads out to sea. Insert the hose into the pipe (it is usually about 30 cm below the surface, so it is possible to do from the dinghy).

Inserted the hose as far as it can go and mark how far it goes. Then take it out and wrap the hose with duct tape or electrician's tape so that the hose seals tightly in the pipe. Then just have one person on the dock by the water tap (where the hose is connected), and another in the bathroom by the shut-off valve from the holding tank.

YACHTING.COM TIP: Another thing our clients often ask is how the toilet (known as a 'head') works on a boat. That's why we've put together a guide on this topic — Marine toilet: how to use it. Take a look to find out what types of toilets you'll encounter on a boat, how to flush it correctly, what you shouldn't put down the head, how to avoid spilling the contents of the tank and how to deal with a blocked toilet.

And, what to watch out for?

So, I fed the hose into the underwater pipe from the dinghy and pushed the wrapped part tightly into the pipe to seal it perfectly. Then I called out to the dock, "Turn on the water!". I felt the water gurgling in the hose and heard the air bubbling in the waste tank. And then I felt some of the contents of the tank, pushed by the water from the hose like a plunger, shoot out through the vent valve located about a metre above my back, and some of the stinky contents fell in a very graceful arc onto my back, ran down my white T-shirt and onto my clean shorts. In an instant, I was covered in smelly excrement.

Disgusted, I yanked the water hose out of the pipe and the fecal matter began to flow rapidly into the clear harbour water. The sea turned brown and I yelled, "Close the tank!". Paul, who was in the bathroom, shut off the valve in a flash and the brown patch stopped expanding. I discreetly sprayed water from the hose onto the patch, dispersing it further away from the boat. In a moment it had all but disappeared. The septic tank was unblocked and I smelt like fecal matter.

I climbed on deck and met Jana who, as I passed her, backed away in absolute disgust and asked why I smelled so bad. So, I told her about my new special deodorant and headed to the shower.

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