How to Clean a Boat Gas Tank: Easy 5-Step Process

Updated February 17, 2022
pump fuel in boat

Is your boat running a bit sluggish? Has it been a while since you've used it? It might be time to clean out your marine gas tank. Are you clueless? Don't worry. You'll learn how to clean out your boat gas tank in no time and how often you should do it.

Easy Method to Clean a Boat Gas Tank

Gas tanks in boats can get gunked up. To know why, you need to understand what happens to boat fuel in a sealed tank. The fuel inside begins to break down chemically, separating into the additives and fuel components. The additives will sink, concentrating at the bottom of the tank as a thick sludge. This is especially true if the gas sat around for a while. Rather than wreck your motor, you can get your gas tank clean with a few steps and supplies.

  • Gas siphon
  • Pressure washer
  • Container for old gas
  • Isopropyl alcohol
  • Sea Foam Engine Cleaner
  • Boat fuel filter
  • Carb cleaner
  • Cloth

Step 1: Drain the Tank

Draining the tank is the first step on your boat gas tank cleaning adventure. If you have a removable gas tank, you can just empty out the gas. However, how you clean a boat fuel tank without removing it is to use a gas siphon.

  1. Remove the fuel cap and plug any vent piping. (Be sure you disconnect your fuel line before where it enters the water filter.)
  2. Stick the hose into the gas tank and put a chemical safe container under the other end of the hose.
  3. Pump the siphon a few times and allow all the gas to drain.
  4. Dispose of the old gas properly since it's toxic.

Step 2: Disconnect the Gas Line to Boat Engine

Chemicals and motors don't mix. So, before you can add any cleaning chemicals to your tank, you need to make sure the gas line is disconnected. Since every boat is a bit different, you might need to check your manual on how you can isolate the gas line.

Step 3: Clean the Boat Fuel Tank

The prep work is done. So, now it's time to get down to cleaning. However, you can do this in a few different ways, depending on what you have available to you.

Pressure Washer

A pressure washer can work well to get dirt, grime, and debris out of the tank.

  1. Using the lowest setting, blast water into the tank.
  2. Use the siphon or dump water out of the tank.
  3. Repeat until water is clear.

Using a Cleaner

You can also use a cleaner like Sea Foam Engine Cleaner or isopropyl alcohol to remove the sludge.

  1. Pour in about ¾ of a can of Sea Foam or fill the gas tank ⅔ of the way up with alcohol.
  2. Allow it to sit in the tank for 15 minutes to several hours.
  3. Dump or siphon the cleaner into a chemical-safe container.
  4. Rinse with water.
  5. Siphon until water is clear.
  6. Ensure all liquid is removed.

Step 4: Check and Change the Fuel Filter

Your gas tank is ultimately going to have some kind of fuel filter. This can look different on plastic and aluminum boat tanks, but it will be there.

  1. Check your fuel filter.
  2. Replace as needed.
  3. Check other parts for debris like gas lines, intake valves, gas caps, and float.
  4. Carb cleaners and other specialized cleaners can be used to remove junk and debris.
  5. Wipe the parts down with a lint-free cloth.

Step 5: Dry the Tank and Reattach Hoses

It's all clean. Now it's time to reassemble.

  1. Use a lint-free towel to wipe everything down as best you can.
  2. If the tank is removable, allow it to dry in the sun with everything open for a few hours.
  3. Reconnect the fuel lines and other parts you might have removed.
  4. Remove any plugs in vents.
  5. Give it a test run.

You can add an evaporator product along with fresh fuel if you are worried about any moisture. You may have to change the filter a couple of times as you run the new fuel through, cleaning out any remaining bits of debris.

Tips for Cleaning Out Your Boat Gas Tank

How to clean your boat gas tank isn't complicated with a bit of know-how. But there are a few things you can do to make things easier.

  • Put the boat on a trailer if possible.
  • For a fixed gas tank, angle the boat so the gas all moves to one side of the tank.
  • Wear protective clothing and gear when dealing with gas.
  • Make sure the area is well-ventilated.
  • Clean the tank regularly to avoid thick slug and buildup. (Especially when you know you will be away from the boat for a while.)
  • For large boats or if you don't feel confident cleaning gas tank, contact a marine professional in your area.

How Do You Know When to Clean Gas Tank?

couple on dock by speedboat

Cleaning your gas tank should become part of your regular boat maintenance. Therefore, you might want to consider cleaning it every six months and at least once a year. You want to make sure to clean it when:

  • Taking out of storage
  • After extreme temperature changes
  • When you buy a boat used
  • If the motor isn't running well

Take Caution When Cleaning Out a Boat Gas Tank

Understand that cleaning out your fuel tank includes cleaning out flammable material. If you have questions or concerns, you should contact a professional. Cleaning your fuel tank should always be performed with safety as the primary objective.

How to Clean a Boat Gas Take With Ease

You should clean the fuel tank on your boat annually and after any extended storage time. Regular cleaning will protect your engine and enhance the performance. Then, you can get on the water with a smile.

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