How To Unblock A Drain On A Boat | Become A Cruiser
How to Unblock a Drain on a Boat

How to Unblock a Drain On a Boat

Sooner or later you are going to have to know how to unblock a drain on a boat. One of the most frequent pop-up maintenance tasks that we have on the boat is unclogging drains.

Generally, a blocked drain is more of an irritation than a real problem. With our fridge drain being the most frequent culprit followed by the basins in the heads.

Our fridge drain seems to block with the slightest amount of anything but water going down the drain. It has a long run and a few sharp turns. Anything dairy seems to be the worst culprit. Spill some milk or cream and it finds its way into the drain. Blocked! It turns to thick sour cream or cheese instantly and can be a real pain to clear.

The basin blockages are normally caused by growth in the pipes or hair. And can be fairly straightforward to clear. At times growth is not the issue but soap scum and that can be a little trickier to clear.

Whatever you do do not try clear any blockage on a boat drain or marine head with a plunger. This is a recipe for disaster as it is entirely possible you blow a hose off of a thru-hull and flood your boat.

If you are looking for how to unblock a toilet on a boat here is a link to the steps involved.

How to Unblock a Drain On a Boat

Here are my eight different methods or steps on how to unblock a drain on boat.

The good news is most blocked drains on a boat are fairly easy to clear. And you can go back to enjoying your beautiful destination in no time at all.

How to Unblock a Drain on a Boat
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Steps To Unblock a Drain On a Boat

Average Time to Clear a Blockage: 15 minutes

Step 1

This is the equivalent of phoning tech support for your computer and being asked if it is turned on.

1. Make sure the seacock is open
2. Make sure there is nothing immediately visible blocking the drain.
3. If it’s a shower drain, hand basin, cockpit drain or scupper first try to use a Drain Snake Hair Drain Clog Remover Cleaning Tool

Step 2

Try Pouring hot water into the drain and giving it time to work. I’ve had limited success with this method unless the drain is blocked due to an oil or grease buildup. This step works to unblock a galley drain but may have limited success with a basin in a head.

Try it. You’ll quickly see where it works on your boat.

Step 3

Don’t put any domestic drain cleaner down a boat drain. These products are far too harsh and will damage components in the boat’s drainage system including composite “Plastic” Thru-hulls.

Another negative of putting something like Liquid Plumber or Draino down a boat drain is that should you have to remove a pipe to clear a blockage you will have to deal with a caustic chemical that is likely to burn you in the process of removing the pipe.

Forget about using an environmentally friendly expensive marine drain cleaner. Most don’t work. Even if they do work you will most likely never find the product again once you leave the US.

Here is my simple cheap recipe for an environmentally friendly drain cleaner for use on a boat.

1. About a 1/2 cup of Bicarbonate of soda
2. About a cup of plain simple white vinegar hot but not boiling

Cold vinegar works too but a little less effective. If you can get high acid vinegar (Pick some up in french countries when you visit) this a bit more potent and better for unblocking a drain on a boat with vinegar and Bicarbonate of soda.

Slowly pour the bicarb down the drain. I use an old chopstick to keep pushing it down the drain if it piles up. Once the bicarb is in the drain pour in the vinegar quite quickly. Put a plug, in the drain or hold your hand/ finger over the drain. This lets the fizzing liquid force it’s way to the blockage.

Repeat alternate between covering the drain and leaving it uncovered. Sometimes the blockage clears up out the drain and other times down the drain and out the thru-hull.

If no success after two tries of an open and then closed drain hole move (four applications of the Bicarb vinegar drain cleaner mix) onto step four. 4 applications of the Bicarb Vinegar drain cleaner mix

Step 4

Time to put on your bathing suit, grab some goggles and a snorkel as you’re going for a swim. Depending on the size thru-hull you need to unblock. Find a large flat head screwdriver or small paint scraper.

If the drain hasn’t cleared by this stage there is some form of marine growth blocking the thru-hull. Normally barnacles. So don’t put your fingers in the thru-hull to feel what is blocking it as they will cut you and you are almost guaranteed an infection.

If you do happen to cut yourself on a barnacle take a look at our article on 8 Natural Remedies All Cruisers Should Know to see how to properly take care of the wound.

Take your screwdriver or paint scraper and carefully scrape any marine growth out from the thru-hull starting at the opening and carefully working in. Be very careful not to damage or “spin” the thru-hull fitting, the pipe, or the sea-cock. The bottom line is to go slowly and gently.

Step 5

If you’ve had no success up to this point take another hose about 1/2 of the diameter of the hose you are trying to clear. Something like a garden hose or pex tubing. It needs to be fairly stiff.

If you’re still in the water work it slowly and carefully up the thru-hull to the blockage. Rotate the pipe every foot so as you push it up. Hopefully, you feel the blockage and can gently break it up.

Try clearing the blockage from in and outside the boat.

Once again avoid being too rough with the pipe as you do not want to force the pipe off of the seacock barb.

Another warning is, as smart as using a wire coat hanger sounds avoid this method as there is a good possibility

a. that it gets stuck in the pipe
b. the more likely scenario that you push it through the soft sides of a hose which could lead to flooding the boat!

Step 6

Caution is the word with this step. If the drain is somewhere that you are not going to wreck the interior of the boat by getting things wet. Bring in the deck wash hose and try to ‘encourage’ the blockage to move with a little pressure.

Place the hose in the blocked drain for a second or two to see if you can get it to clear. This is the only method that works on our fridge if milk or cream goes down the drain.

This is a bit of a contradiction to the plunger warning as you will be adding pressure. Just that it is quite a bit less than you get from a plunger.

Be careful and keep checking that you are not blowing off any joints or pushing the pipe off of the seacock.

Step 7

You’re having a bad day if you’ve got this far and the pipe is still blocked.

1. Close the seacock.

2. Remove the pipe and clear it by banging. You can try a metal coat hanger in this step as you will see if you are causing any damage (don’t use a coat hanger on any hoses that are connected to an open seacock as there is a risk of puncturing the hose.)

If it clears reinstall it and open the seacock.

If not, common drain hose sizes are easy to find just about anywhere in the world. Change out the hose. Preferably with a smooth bore hose.

How to Unblock a Drain on a Boat
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Hi, I’m Nic! Our Family of four have been out cruising since 2016. We have sailed about 15,000nm, almost halfway around the world. We sold everything, took the leap of faith, and bought a 10-year-old Lagoon 380 ex-charter catamaran. We’ve fixed every system on the boat, often more than once. Cruising has been such a wonderful, positive experience for our family that I want to share my tips to help you Become a Cruiser.

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