How to Clean a Boat Gas Tank Without Removing It (4 Steps)

A well-oiled, well-maintained machine ensures that every trip out to the water will be safe and problem-free. But you might notice that after a bunch of boat rides, your pontoon just might not work the same way it did when you first brought it home from the dealership. A sputter here, a stutter there. What gives?

While there are a bunch of problems that could cause less than optimal performance, one simple maintenance trick that might get your boat running like brand new would be to clean out your gas tank. Don’t sweat it - there’s no need to take it out. Here’s a quick guide on exactly how to clean a boat gas tank without removing it.

The Essentials for Cleaning a Boat Gas Tank

Before you get started, you’re going to need a bunch of gear, equipment, and cleaners to get the job done as safely and efficiently as possible. That said, see to it that the following items are on hand before you begin:

If you don’t have work overalls and don’t really think you need to buy a set, make sure you wear clothes that you don’t mind tossing out after your cleaning project. Gasoline (and the gunk that goes with it) can easily soil and stain clothes.

The Gas Tank Cleaning Process

Now that you’ve got everything ready, it’s time to get right to it. Even if it’s your first time cleaning out a pontoon boat gas tank, you should be able to do it successfully and efficiently as long as you follow through with these steps.

1. Position Your Pontoon

It’s imperative that you find the right place to clean your gas tank since you’re going to be handling some pretty dangerous chemicals. The best place to get the job done would be an open, well-ventilated area with lots of bright light and almost zero obstructions.

Other than that, you’re going to want to position your pontoon in such a way that it’s sitting on an incline. This just makes it easier to get out any excess fuel by allowing gravity to work its magic and pool the gas to one side for efficient collection. At this point, you’re also going to want to don your PPE.

2. Siphon the Excess

Now that your boat’s positioned and you’re dressed for the part, it’s time to siphon out the excess. In movies, you’ll typically see people sticking a tube in the gas tank, sucking the opposite end, and then welcoming a stream of colored yet otherwise clear fluid and then spitting out a mouthful of the rest.

While that might look super cool, it’s not recommended that you try it at home. Gasoline is a highly toxic chemical, and there’s a lot that could go wrong with taking in a mouthful even if you decide to spit it out.

The length of time it takes to siphon out the contents of your tank ultimately depends on how much it contains. Remember though that it’s unlikely for you to be able to get every last drop especially if there’s sludge at the bottom of the tank.

See to it that you position your collection container right under the exit tube of your siphon pump. If you’re not entirely sure how much gas you’re expecting, make sure you have a spare chemical-safe container at the ready.

3. Clean the Sludge

Once all of the gas is out, you can then proceed to clean what’s left. But before you toss any chemicals into the tank, make sure you cut off the lines that feed into your engine. If you don’t isolate the lines, you could introduce cleaning chemicals into your engine and cause major damage.

When that’s out of the way, you can then add in some motor treatment. See to it that you read the instructions and add in the amount that the bottle indicates. In the absence of a motor treatment product, you can use isopropyl alcohol.

Let it sit for a few minutes to get it to complete the cleaning job. The chemicals should react and make the accumulated sludge easier to get out. After a few minutes, you can siphon out the contents of the tank once more.

If you’re not entirely confident that the tank has been completely cleaned, you can use a high-pressure washer to get all of its interior. A specialized tank cleaning nozzle should make it possible for you to remove caked on gunk in hard to reach areas. Drain with your siphon when you’re done.

4. Dry Out and Protect

Leave the gas tank open to allow excess moisture to evaporate. Once you feel like it’s as dry as it can possibly get, you can then add in some fuel tank cleaner. The purpose of this cleaner is to improve combustion and thus fuel economy, allowing your pontoon to use every drop of fuel in the tank.

It also removes water and makes it harder for aged gasoline to form into gunk over extended periods of sitting in your garage. Use the chemical as state on the bottle directions since different products tend to call for varying amounts.

When Is It Time To Clean a Gas Tank?

No one really tells you when it’s time to clean a gas tank, so as a boat owner, you should be able to identify the opportunity before you run into any issues with your boat. In general, you’re going to want to clean your gas tank when:

Your boat has been in storage for too long, especially during the winter

Long periods of storage can change gasoline chemistry. Add in the ever changing temperatures, and it’s really only a matter of time before that gunk starts to form. That’s why most boat owners include gas tank emptying in their list of winterizing steps.

It's been one or two years since your last fuel tank cleaning

You don’t really need to clean your gas tank every month - that would be overkill. But if it’s been a year or two since you last cleared out the sludge, then it would probably be a good idea to give it a thorough cleansing.

Your boat is using more fuel than it usually does

When sludge builds up and coats your gas tank, it becomes harder for the good stuff to combust. That gunk also invites more fuel to cling and form sludge, which means every time you gas up, a portion of your fuel goes to sludge.

Your boat doesn't work as smoothly as it did before

Sputtering, stuttering, and the sounds of an overworked engine may mean that there’s stuff getting in the way of clean combustion. Before you head off for an expensive trip to the maintenance guys, make sure you try cleaning out your gas tank first -- that might be all your boat needs.

How Do You Clean a Removable Boat Gas Tank?

A removable plastic gas tank’s purpose is to hold emergency fuel. Since they’re not designed to be as secured and sealed as a fixed tank, they can accumulated filth over time. Drain the contents over a sieve to get rid of any contaminants in case the fuel is still good to use.

But gas that’s been phase separated should not be reused and must be responsibly disposed of. This happens when gas sits too long in a tank, forcing its contents to separate into gasoline, ethanol, and water. There’s no way to save separated fuel, so make sure to dispose of it properly.

To finish up the cleaning process, throw in a few nuts and bolts and add a dose of acetone. Seal the can and shake it around -- the bolts should work to knock off gunk and sludge that may have accumulated around the inner walls of your tank.

Get rid of what you collect (and dispose properly of course) and let the tank air out. You can also give it a spritz of water, but make sure you allow all the moisture to evaporate before you load it up with fuel.

When’s The Last Time You Cleaned Your Gas Tank?

There are a lot of boat maintenance tasks you can do at home to save up on costs, and gas tank cleaning is one of them. So the next time you find yourself wondering how to clean a boat gas tank without removing it, visit back here.

Just make sure to come prepared with the right gear to get the job done as smoothly as possible. And it doesn’t hurt to read up on proper care and disposal in case you collect gas that’s separated or just too old to reuse. This way, you can be sure to toss your waste properly to protect the environment according to your local rules and laws.