How To Clean A Boat Fuel Tank

Paul Luisi
by Paul

Every boat owner will go through the task of cleaning the boat fuel tank at some time.

But how do you clean the tank properly without contamination?

These instructions apply to boat owners of inboard and outboard motor engines like sailboats, motorboats, catamarans, yachts, pontoons, speedboats and trawlers.

This guide highlights how to clean contaminated fuel tanks, remove sludge, unclog fuel lines and rejuvenate old gasoline and diesel fuel.

In order to clean a boat fuel tank, follow the steps:

  1. Drain The Fuel Tank
  2. Isolate The Lines From Tank To Boat Engine
  3. Remove Old Fuel Filters
  4. Pressure Wash Fuel Tank & Remove Dirt
  5. Reattach The Fuel Tank Hoses & Lines
  6. Fill Tank With Clean Fuels
  7. Start up motor and leave idle for 10 minutes

Some boats will have specific instructions when cleaning the fuel tank.

Check the boat owners manual for instructions specific to your boat.

The goal is to have a sparkling clean tank and remove any fuel-tank contamination and rust.

Cleaning out a boat's fuel tank is a relatively simple process once done correctly.

Step 1: Drain The Fuel Tank

To drain a boat fuel tank: 

  • Use a fuel suction pump and a bucket to pump fuel out of the tank.
  • Fill the bucket with the fuel from the engine and ensure all bulky dirt is also pumped out of the tank.

Draining the fuel tank should take 5 - 10 minutes to complete depending on how large the tank is.

The how to remove bad fuel from boat fuel tank guide will also help with safely removing dirty and contaminated fuel.

Draining the fuel tank can be done with a simple fuel suction pump and bucket. It should take no longer than 5 - 10 minutes.

Step 2: Isolate the Fuel Lines From Tank To Boat Engine

Every boat motor is different so check the boat engine manual for specifics on individual boats.

Isolating the fuel lines from the tank to engine will:

  • Stop leakage of fluids:  Fill a bucket with any trapped fluids in the fuel lines.
  • Stop water getting into the engine: Isolating the fuel lines will help stop the water you use to clean the tank from getting into the engine.
  • Help find and remove trapped dirt: Sometimes there is a build up of dirt in the actual fuel lines that you can easily clean when you remove the lines from the engine.

Disconnecting the fuel lines from the engine will help prevent fuel tank contamination and engine damage.

Disconnecting the fuel lines will prevent water getting into the engine when cleaning. It will also help remove dirt build up in the fuel lines.

Step 3: Remove Old Fuel Filter

Remove the old fuel filter from the boat motor. The fuel filter will typically have a build up of dirt.

Once the fuel tank is clean (after following the steps below), replace the old one with a new fuel filter.

Replacing a fuel filter is a quick and easy step in removing dirt from the fuel tank.

Step 4: Pressure Wash Fuel Tank & Fill With Sea Foam Cleaner

Use a hot pressure washer to blast any hard to get dirt, sludge or residue build up in the fuel tank.

Do not attempt this without having all the connecting fuel lines disconnected first.

After pressure washing the tank: 

  • Fill Fuel Tank With Sea Foam Cleaner:  Let the sea foam cleaner sit in tank for some time. This will help dissolve any remaining dirt.
  • Remove cleaner fluid with fuel suction pump: Use the fuel suction pump to remove the sea foam cleaner and all fluids from tank again.

The sea form cleaner will remove the toughest dirt from the fuel tank.

Pressure wash the fuel tank with warm water. After that, fill the tank with sea foam cleaner to remove tough dirt and sludge. After letting it sit, use fuel suction pump to remove all liquid.

Step 5: Reattach Fuel Tank Hoses & New Fuel Filter

Once everything is clean and the boats fuel tank is dried out (it's important to have the tank empty of any fluids), reattach the fuel lines.

Install the new fuel filter too.

Remember if you haven't cleaned the tank in some time to ensure the hoses/filters are spotless too.

Follow the users manual for this step to ensure the fuel lines are re attached in the correct way.

Step 6: Fill Tank With Clean Fuel

Whether it's diesel engine clean fuel or any other gasoline marine engines fuel, it's good practice to feed your boat engine with the fuel it needs.

This will have lots of benefits including improved boating performance, it will help with fuel-system maintenance.

Just look at the image above to see the obvious difference a cleaner fuel tank will have on the fuels versus a dirty one.

Fill the tank with fresh clean fuel for the boat engine.

Step 7: Start Up Motor & Leave Idle

When the new fuel is in the fuel tank, start up the engine and let it run idle for a few minutes.

This will make sure the reattaching of the fuel lines and cleaning worked and there are no issues with the motor.

Start up the engine and let it run for a few minutes to make sure everything is running properly after the clean.

Boat Fuel Tank Cleaning Products To Use

When cleaning a boat fuel tank, the equipment needed is: 

  • Fuel suction pump
  • Bucket
  • Fuel tank cleaner
  • Fuel Treatment Solution
  • Fuel Filter

These items should be sufficient for cleaning a boat fuel tank.

We recommend checking the list of the best boat fuel tank cleaning products to help ensure the right items are used to clean the tank.

Ongoing Boat Fuel Tank Cleaning

As part of regular fuel tank maintenance, use a fuel system cleaner to mix with the fuel in the boat engine.

This boat fuel cleaner will help prevent contamination of the fuel.

It will also protect against a build of dirt and sludge in the future.

Regularly cleaning the fuel tank is great for keeping the fuel flow running efficiently.

Check the benefits of cleaning a boat fuel tank for all the advantages of keeping the tank clean on an ongoing basis.

Alternative Fuel Tank Cleaning Options

When looking to clean a boat's fuel tank, there are other options available: 

  • Hire a fuel tank cleaning company: A boat cleaning company will come and clean the tank for you. The cost of cleaning a boat fuel tank ranges from $45 to over $300 for larger boats.
  • Hire a professional to clean the tank: Find a professional on thumbtack or craigslist to wash and clean out the fuel tank.

These options are best for those that want to outsource the cleaning work.

How To Clean Boat Fuel Tank Video Instructions

Below is a video from thatboatguy on a simple diy version of cleaning your boat fuel tank.