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How To Drain Diesel Exhaust Fluid

In theory, you should never have to drain your vehicle's diesel exhaust fluid. But if your DEF tank has become polluted from dirt, pollen, or other elements, you'll find that draining and refilling it with new fluid is necessary. If you are wondering how to accomplish this, we can help. We researched diesel exhaust fluid tanks from multiple professional sources, so you'll know what steps to take.

The most effective method to drain diesel exhaust fluid is to use an approved siphon. You will be able to drain the fluid by:

  • Installing the siphon
  • Pumping the siphon until it begins to empty the diesel exhaust fluid
  • Filling the tank with new diesel exhaust fluid

Now that we know the steps for training a diesel exhaust fluid tank, we'll look at each in more detail. You might also wonder if diesel exhaust fluid can be dumped down the drain or a vehicle can work without this fluid. For the answers to these questions and more, read ahead in this post to see what our research has uncovered.

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The hands of a young caucasian man in a yellow jacket hold a refueling gun in the tank on a green car, How To Drain Diesel Exhaust Fluid

A step-by-step guide to draining your diesel exhaust fluid tank

Getting contaminated fluid out of your diesel exhaust tank is easy. You will need to purchase a good siphon, which can be found at almost any automotive parts store. You will also need a gas can, rags for clean-up, and a new diesel exhaust fluid.

Once you have your supplies gathered, you'll be ready to begin.

Refueling nozzle inserted into the tank on a green car with a red taillight at a gas station

Install the siphon

Open the cap to the diesel exhaust fluid tank. It will be to the right of your fuel cap. Carefully insert the siphon into the tank. It should be inserted until it begins wrapping itself in the tank's bottom.

Check all of the fittings to make sure that they are not loose. If they are, they will leak the fluid when you begin to siphon. So double-check to make sure!

Once the siphon has been fully inserted into the tank and the fittings checked, you'll be able to remove the fluid.

Pump the siphon until it begins to empty the diesel exhaust fluid

Run the other end of the siphon into a gas can. As many diesel exhaust fluid tanks are five gallons, you'll want to make sure your gas can is at least this big.

Gently pump the siphon until a steady stream of diesel exhaust fluid begins to be expelled into the gas can. This can take a bit of time to empty, so be patient.

When the tank is close to being empty, the stream of fluid will begin to slow considerably. You may have to wiggle the siphon hose so that it can get more fluid into it.

Fill the tank with new diesel exhaust fluid.

Once your tank has been drained, you can put new diesel exhaust fluid into it. Using a funnel, carefully pour the new fluid into the tank. Once full, be sure to tighten its cap.

Start your truck and drive it to make sure that your diesel exhaust fluid light comes off. It should stop illuminating after no more than 30 miles.

Use the rags to clean up any spills or drips.

Properly dispose of your contaminated diesel exhaust fluid, and you're all done! 

For a video tutorial on how to siphon the diesel exhaust fluid tank, watch the one below:

Can diesel exhaust fluid be dumped down a drain?

You might be tempted to just dump your old diesel exhaust fluid down the drain in your garage when you need to dispose of it. Many of the fluids from your vehicle pose a serious risk to the environment if you do this. So does diesel exhaust fluid have the same negative impacts?

Composed of 65 percent distilled water and 35 percent urea, diesel exhaust fluid is not classified as a hazardous material. Urea is a fertilizer derivative, which doesn't make it necessarily harmful to the water table if it's dumped down a drain.

But while experts insist that there are no prohibitions on this sort of disposal, many still urge you to take it to a landfill and pay to have it disposed of there. Most sanitary landfills will have a system of getting rid of agricultural chemicals to which urea technically belongs. This can be done at a minimal cost, as you usually won't be disposing of more than five gallons at a time.

Can my vehicle work without diesel exhaust fluid?

If your vehicle has a diesel exhaust fluid tank, you will need to keep this fluid handy. You will get a warning light on your instrument cluster if the tank gets too low. If you ignore this warning, your truck will begin to slow itself.

When your tank gets below 10 percent, the warning light will illuminate. If you let it fall below 2.5 percent, the onboard computer will begin to brake the vehicle. While it won't make your truck come to a complete stop, it will slow you down to five miles per hour. 

This will not remedy itself. If your fluid gets too low, you will have to add more to get it running efficiently again. Always keep some diesel exhaust fluid handy and add the appropriate amount as soon as possible after your warning light comes on.

Car dashboard icons

How long is diesel exhaust fluid good for?

How long this vital fluid will keep depends on a few factors. But if it is stored properly, you can expect it to last about two years on the shelf.

Keeping it in the original container, whether it's in a drum or otherwise, is essential. This keeps contaminants from invading the fluid, decreasing the useful shelf life. Any spot out of the sunlight will also greatly help get the most life out of this fluid.

A controlled environment also helps this fluid last. Avoid places where the temperatures and humidity levels greatly fluctuate, ideally keeping it at a temperature of 75 degrees. You should consider the fluid unusable if it has been in your possession for three years or more.

Diesel exhaust fluid or DEF sign posted in a truck stop, next to fuel pump

Should I keep my diesel exhaust fluid tank full?

While it isn't necessary to keep your diesel exhaust fluid tank full all the time, it's a good idea to check its level routinely. This fluid will be used regularly and must be replenished relatively often. As it is mostly water, it is also subject to some evaporation. So how quickly it leaves the tank will also depend on the climate.

We suggest checking the level of this fluid every time you leave for a long trip. If your trips are shorter, it's a good idea to check the levels every time you fill up, adding more if necessary. The last thing you'll want is your warning light to come on in the middle of a trip, forcing you to find more of this vital fluid.

School bus def only sign close-up

Final thoughts

The hands of a young caucasian man in a yellow jacket hold a refueling gun in the tank on a green car

Diesel exhaust fluid can become contaminated, forcing you to drain its tank and replace it with fresh fluid. Doing this is a straightforward process requiring minimal skill and only a siphon and a disposal container. Be sure to keep the diesel exhaust fluid tank levels up, or it will result in your vehicle being forcibly slowed by your onboard computer. Drive safe!

We hope this post on Diesel Exhaust Fluid answered all of your questions. For more helpful information, we suggest reading the following posts:

What's' The Best DEF [Diesel Exhaust Fluid] For Ford F250?

Does DEF Go Bad? [Inc. If Frozen]