Gray Water Tank Smells Like Rotten Eggs: What To Do

The last thing you want to smell in the great outdoors is rotten eggs, especially if it’s coming from your RV or travel trailer.

Since your gray water tank is holding dirty water, with food particles, it is a breeding ground for odor-causing bacteria.

This post will review the common causes and ways to prevent this rotten egg smell, including:

  • What causes the bad smell
  • How to get rid of the sulfur smell
  • How to prevent the bad smell

To treat your grey water tank, you can use bleach or vinegar to kill bacteria. And to prevent this from ever happening, things like keeping your stack vent clear and flushing your holding tank will help.

Table of Contents

What is that Rotten Egg Smell?

The rotten egg smell in your RV is not pleasant. It makes your camper uncomfortable and embarrassing should you have visitors. 

What makes it more difficult is trying to find the source of the sewer smell. I spent many times sniffing around my RV to find the source of the foul odor. With the small space of an RV, it can be a challenge as the whole space fills up quickly, and tough to determine the source of the unpleasant smell. 

First, determine that you don’t have a propane leak. The rotten egg smell is also a sign of a propane leak. It is important to determine that you are not dealing with a propane leak as this is a more immediate fix and safety concern. 

Hydrogen Sulfide

Hydrogen sulfide gas is the unpleasant odor when smelling rotten eggs from your gray water tank. This gas is caused during the decomposition process in the absence of oxygen. 

This can be caused in your RV tank because there is stagnant water with little to no oxygen, and the decomposition of whatever goes down your drain. As water sits stagnant in your holding tank and there is a breakdown of whatever goes down your drain, the sulfur bacteria gives out a sulfur odor. 

Causes of Odor

So what is causing this foul odor, and why is it in the grey water tank? The simple answer is that you have stagnant water in a tank with food (from your kitchen sink), soap, and bacteria from your body. 

Holding tanks are breeding grounds for odor.

This bacteria and odor are also compounded after many uses of your RV. Even when you drain your grey tank, the tank itself is not thoroughly cleaned, and there is usually some old smelly water left in the tank. This cycle will cause the bacteria and gas to be created quicker with each use. 

Plumbing Vent

Your camper water system is very similar to a house plumbing system. There are a series of traps and vents to expel any sewer gas to the outdoors.

Your RV is no different, and the same principles of water and gas still apply. You have a stack vent, which acts as a chimney through your roof to eliminate any foul order. And you also have P-traps at your sinks and tubs that use water to keep sewer gas coming indoors. 

How to get rid of the sulfur smell

Since the issue is bacteria and water, the first step is to see the options to treat the water. Since this is grey water and not a freshwater tank, we have some good options that won’t affect anything with drinking water. 


Bleach kills everything, and this case is no different. If you have that rotten egg smell in your holding tank, give a splash of bleach down one of your sink drains. It does not take much to sanitize the water to eliminate the odor, so start with a 1/4 cup and see if that does the trick.

One tip is to premix the bleach with a gallon of water. You can pour a quarter gallon of the diluted solution into your sinks and bathtub. This will also help sanitize the water in all of your P-traps.


Vinegar is an acidic liquid made from apples and grains and contains acetic acid. This acetic acid has natural antibacterial qualities, which make it a great alternative to chemical cleaners when cleaning around your RV.

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Although not as strong as bleach, vinegar will also help eliminate the unpleasant odor. Start by trying one to two cups of vinegar. If you notice only a slight improvement, give some vinegar as needed.

The quantity of vinegar is challenging to calculate because it depends on how much water is in your holding tank. A cup of vinegar should do the trick if you only have a few gallons. If you have over 15 gallons of water in your tank, a couple of cups may not be enough. You will need to judge this amount and see what works.

Grey Water Odor Control

There are specific products you can also buy that are specific to grey water odor control. I have used the Thetford brand of odor control, and it works pretty well. The directions have you add about 1/5 of the bottle for every 40 gallons. This is a good solution if you have some nearby and want to use a product specifically formulated to control the gray water odor.

Thetford makes a product for odor control

RV Toilet Treatment

Did you know you can also put that blue toilet treatment in your grey tank? You can dump some down your sink drain if you have liquid deodorant for your toilet. This chemical is designed to break down paper and waste. Although that is not needed with your grey water, it also deodorizes, which will help with the smell.

I prefer bleach or vinegar, but if you don’t have those in your RV, you can try the RV toilet chemical. If you have the pod toilet chemical, that just won’t work, and I suggest you stick with just the bleach or vinegar.

How to Prevent the Bad Smell

Most of the time, prevention is the best solution to a problem. And in this case, here are a few tips to help prevent the situation of rotten egg odor.

Check Stack Vent

Your RV stack vent acts like a chimney to exhaust any bad smell from your gray tank. This stack vent is connected to your tank and is a pipe that goes up through your roof. The pressure difference from the low point of the tank to the high point of the pipe creates suction up and out of the tank.

Sometimes a stack vent can be clogged or filled with debris. Check your stack vent and ensure it is free and clear from blockage. Any obstruction will not allow the pressure to build up and exhaust the bad smell.

Keep P-Traps Full of Water

At each of your sinks, you have a P-trap. This P-trap is nothing more than a bent pipe, usually in the shape of a “P”, where water collects and acts as a stop for gases. Think of that water like a cork that keeps the gases from escaping.

Under normal sink usage, the P-trap is constantly filled with RV water and will work properly. P-traps can fail if sinks or tubs are not being used and the water evaporates. If the water evaporates, then there is no water to stop the gas, and you will likely smell all the gas from your gray holding tank.

P-trap is full of water to keep out gases

The common area for this evaporation is the tub or shower. If you do not use your tub or shower often, the P-trap water will evaporate and cause the gases to come into your camper.

A solution to this evaporation is to turn on the faucet every couple of days so the P-traps will have water in them to block out the gases.

Drain plug

Using a drain plug will help keep out gases in a couple of ways. The first way is that it will keep the P-trap from evaporating. This will be helpful in areas such as your tub or shower if it is not used often.

Another way a drain plug is helpful is that it will help cap off the gas coming into the camper. If you have a P-trap full of water, it should stop most, of the gases. However, if there is a slight issue and some gas is getting through a drain plug could help keep the gases in the tank.

Fully Drain Grey Waste Tank

Next time you dump your grey waste tank, ensure all the water is drained. Then, fill the tank again with as much water as you can. Putting some bleach in this water will also help. Once full with bleach water, drain the tank. This should have somewhat sanitized your tank and expelled most of the bacteria causing the rotten egg smell.

Since there is no good way to get water pressure in your grey tank, this is the best method to clean it. Unlike a black water tank that has a hose connection for water pressure, a grey holding tank can only have access to gravity-fed water.

Final Thoughts

There are a few options to treat your gray water tank. Using bleach or vinegar helps kill the bacteria causing the sulfur-smelling gas. Doing things to prevent the odor, such as using drain plugs and cleaning your water tank will help.