How to Drain Old Gas From Your Boat's Fuel Tank

Draining old gas from your fuel tank is an important step in boat maintenance, as it helps prolong the life of your tank and keeps the engine running smoothly. When it does come time to take your boat out of the water for the season, draining the fuel tank can prevent residue build-up in the off-season. But how exactly do you empty your boat’s fuel tank, and is it something you can do yourself?

Every boat enthusiast knows that boating and fishing can be an expensive hobby, so learning to drain your fuel tank will help you save some expenses. Here, we'll cover the tools you need to successfully drain your fuel tank and the steps necessary to do it on your own. 

The Tools You’ll Need

Siphoning old gas out of a boat fuel tank can be done relatively cheaply, depending on the type of fuel pump you use:

• Manual Fuel Pump. There are different types of manual pumps, which are typically sold as kits at your local marina store. As the name implies, you have to run the pump manually to drain old gas from your boat’s tank. This is a good choice for those who only need to drain their boat's fuel pump occasionally (once a year, before the off-season, ideally). Most kits also come with a 3/8-inch fuel hose. If the kit you buy doesn't come with a hose, you'll need to purchase one separately.

• Electric or Battery Pump. An electric pump is much easier and more efficient at draining a fuel tank, but these are a bit pricier. Good electric and battery-operated pumps can range anywhere between $150 and $300. For an electric model, you do need an extension cord to drain the tank.

You will also need somewhere to securely store the old fuel as it's draining. Make sure you have an appropriate fuel container or gas can handy, which is large enough to capture all of the fuel as it's being siphoned from the tank.

Finally, it's a good idea to wear basic safety gear when handling boat fuel. Depending on your comfort level, you'll likely need a pair of rubber gloves. Fuel is a skin irritant, so you'll want to avoid letting it come in contact with your skin. A pair of goggles is also a good idea. If the smell of fumes from gas bothers you, a face mask can help, as well.

How to Drain Gas from the Fuel Tank: Step By Step

Step 1: Run the Boat if Necessary

Depending on how much gas is still in the tank, you may want to run your boat to reduce the fuel level further. Less than 1/8 of a tank is a good range to have on the boat's fuel gauge before draining it. If necessary, go for a quick ride before draining your tank.

Step 2: Remove Your Boat from the Water

Whether you have a lift on your private dock or boathouse, or you opt to lift your vessel onto a trailer, you will need to remove it from the water to properly drain the fuel tank.

Step 3: Put on Protective Gear

Make sure you’re wearing your safety gear and that your boat is in a dry, well-ventilated place.

Step 4: Position Your Fuel Container

Whatever type of receptacle you opt to use to store the old gas, it needs to be lower than the boat's fuel tank for the transfer process to work. It will also need to be within range of the hose.

Step 5a: How to Use a Manual Pump

If you're using a manual pump, submerge the suction pump in the gas tank. The pump should be attached to the hose, so just make sure you have enough slack to reach the bottom of the tank. Put the other end of the hose in the container you're using to catch the fuel. Start operating the manual pump until fuel starts freely flowing through the hose. The tank should fully drain within a few minutes, depending on how much fuel is in it.

Step 5b: How to Use an Electric or Battery Pump

An electric pump will also have a suction pump attached to a hose at one end. Submerge the suction pump into the tank and put the other end of the hose in your container. Flip the switch on the pump and allow it to completely drain your tank. If the steps are slightly different in the owner's manual for the electric or battery pump you've chosen, follow those steps exactly.

Other Options - Use a Fuel Stabilizer 

Draining gas from your fuel tank is one option, but using a boat fuel stabilizer might be a better choice for some people. A stabilizer neutralizes free radicals in fuel, so it won't gum up the engine if you need to store your boat for a few weeks or months. It will also make it easier to restart the engine when the next boating season arrives.

Why Fuel Stabilizer is a Smart Choice for Off-Season Storage

Prevents Fuel Breakdown: Marine fuel degrades over time. This can form gum deposits in your engine, leading to expensive repairs. A boat stabilizer for fuel prevents this.

Prevents Against Ethanol Damage: Ethanol in fuel attracts moisture. This can lead to phase separation in your fuel tank when the ethanol sinks to the bottom. This can corrode metals in your engine and may even prevent it from starting.

Easier Than Draining the Tank: Many boaters swear by using marine fuel stabilizer because it's a much easier and faster process than draining the fuel tank.

Ensures a Smooth Start in Spring: When your boat's engine and fuel tank sit empty for a few weeks or months, it can be difficult to get it to restart. You run the risk of clogged fuel lines or engine issues over time, especially when the boat is stored empty for a longer period.

How to Add Fuel Stabilizer to Your Boat’s Engine

1. Choose the Right Fuel Stabilizer

Marine fuel stabilizers are designed to combat ethanol-related issues. If you use any old fuel stabilizer, it might not be properly formulated for this task. The product label should help you figure out the correct dosage based on the capacity of your boat's fuel tank.

2. Add the Fuel Stabilizer

Read the manufacturer's label and add that much boat fuel stabilizer to the tank, based on how many gallons of fuel it holds. You want to do this BEFORE your final fill-up of the season to ensure that the stabilizer is properly mixed with the fuel.

3. Fill Your Fuel Tank

Refill your fuel tank to around 95 percent capacity. The less room you leave in the tank, the less chance there is for condensation and moisture to build up inside it. Don't top the tank off, however. You want to leave some room to account for slight expansion of the fuel when the boat is in storage.

4. Run the Engine

Now that the fuel and stabilizer are mixed, start the engine. Let it run for 10 to 15 minutes, or longer if the manufacturer recommends it. This will circulate the now-treated fuel throughout the engine's systems. If you have auxiliary systems like generators that also use boat fuel, it's a good idea to run some stabilized fuel through them as well.

5. Store Your Boat Properly

Store your boat in a dry area with plenty of ventilation to reduce the risk of any moisture build-up during the off-season. This is a good time to use other winterization techniques, too. Apply fogging oil to the engine's intake, check the lines for fuel leaks, change the oil and filter, and so on.

Protect Your Engine with Top-Quality Fuel Stabilizers

By preventing fuel degradation and protecting against moisture, you set the stage for a seamless return to the water. Remember to properly dispose of old gas at your local hazardous waste disposal center and thoroughly clean the hoses on your fuel pump to prevent any potential ignition from residue. With these simple steps, your boat's fuel tank will be clean, protected, and ready for extended longevity during the off-season.

At Gemlux, we’re here to provide you with pro tips for keeping your vessel in ship shape year-round. To learn more about how to install and store boating and fishing equipment, as well as care for and properly maintain your vessel, check out our videos!