Why Does My RV Toilet Smell When Flushed?

A stinky toilet is unbearable in the tight confines of an RV. Your toilet’s lingering sewage-like smell is probably seeping up from the black water tank. This isn’t normal. Well-maintained RV toilets don’t stink.

Why Does the Toilet Stink Like Sewage After Flushing?

Your RV toilet connects directly to the black water tank. There will always be anaerobic decomposition since the waste tank contains poop and bacteria. This decomposition creates the trademark sewage smell.

Residential toilets never smell like sewage because they have a P-trap or U-joint water trap. This is the permanent bit of water that sits in the toilet bowl even after flushing. 

The water creates an air-tight seal between the plumbing and the toilet bowl to prevent sewage gases from leaking into the house.

Most RV toilets don’t have the p-trap or water-filled U-joint. They have a simple flap that opens when you flush and closes immediately after. This makes it easier for odors to seep from your septic tank bank into the RV every time you flush the toilet.

Nonetheless, a flushable RV toilet shouldn’t smell that much because you deal with a smaller waste storage tank emptied frequently. The gas buildup shouldn’t be as much as in a house setting.

Keep Your RV Toilet VERY Clean

Keeping your toilet clean is the first step to getting rid of lingering smells. Most RV toilets are plastic, a material that isn’t as resilient as porcelain on traditional toilets.

Dirt and smell linger on plastic longer. The more you wait before cleaning the toilet, the stronger it becomes. Combine this with the brief gas backflow when you flush and get an overwhelming stench.

Naturally, you will link the now powerful smell to flushing the toilet. Though right, it is only stronger because your toilet bowl already had another lingering smell.

Use a toilet brush and your favorite toilet cleaner to scrub your RV toilet at least once a day. This will keep secondary smells down while retaining its original color and a hygienic sheen. 

So, Why is the Sewage Smell So Strong?

The inherent design flaw in your RV toilet doesn’t mean that the sewage smell should permeate your entire motorhome every time you use the toilet. A couple of other problems escalate to levels the alternative bowl seal flap cannot handle.

The top things you should consider when troubleshooting a smelly RV loo include:

Your Black Tank’s Vent Pipe is Blocked

Every RV should have a vent pipe from the very top of the blank water tank. The pipe snakes to an opening to the RV roof, allowing gases in the tank to escape into the environment away from your living space.

All those inevitable gases sit in the RV if the vent is blocked, waiting for an alternative way out. A well-vented tank will never generate enough backpressure to push gases into your toilet bowl when you flush.

In most cases, the sewage smell in your RV is because it has nowhere else to go. Before going further with the troubleshooting, ensure that your black water tank:

  • It has a vent (especially if it is a DIY converted camper)
  • The vent isn’t blocked

How to Unblock a Black Water Tank Vent

After a paint job, leaves, tree debris, bird nests, and even masking tape can block your vent. A visual inspection and a cleanup attempt is the only way to ensure your vent is open.

RVs have two vents. One for the grey water and one for the black water tank. Some combine the two vents into one roof vent, while others remain independent.

Regardless of the approach, the inspection and cleaning procedure will be the same.

  • Confirm that the vent hole on the black and grey water tanks is connected to a pipe or hose. If they’re not connected to anything, then you have no working roof vent
  • Get a ladder and climb onto your RV’s roof. Be careful not to fall or step on unreinforced parts of the roof
  • Identify the black water tank vent and the grey water tank vent
  • Do a visual inspection to ensure that there’s no tape or any other obvious obstructions on the vent
  • Remove any weather cap on the vents and run a garden hose into the vent. It doesn’t have to go very deep
  • Turn on the water to the hose and listen to your black water or grey water tank to see if the water is making its way. There is a steady flow
  • If you can hear the water, check the other tank. Maybe you got the wrong vent. If you can’t hear it in any of the tanks, then you have a blockage
  • The water could also be leaking from the top of the vent around the hose if it is blocked

Once you identify a blockage, you can use the garden hose and some water pressure to push the blockage down into the waste tank.

Alternatively, you can use a wire snake to pull the clog out through the top of the vent. If none of these tricks work, consider getting an RV shopping to follow up on the vents and find the blockage.

ProTip: Though very rare, your waste tank vents could be cranked or disconnected. In this case, the water could leak somewhere into the RV. Be careful when running this test.

You Have a Damaged Toilet Bowl Seal

Your toilet has a spring-loaded flap (or foot-operated) that opens as you flush to let the waste out and reseals once all the water is gone.

The flap sits against a seal to create a relatively airtight fit preventing the black water tank smell from seeping back into the RV.

Over time, this seal can get worn out and no longer form the perfect seal with the lid. This will let sewage stench seep back into your toilet.

The RV toilet could also have another seal at the bottom where it attaches to the RV floor. Any damage to this seal or a warped RV floor will cause leakages at this point. You will have both a water leak and a foul-smelling gas leak.

The Solution

Replace the damaged seal. If you drive an old RV or use a salvage RV toilet, your unit wasn’t designed with an efficient toilet seal.

Most post-2014 have dedicated seals that keep all the gases away, stopping the sewage smell from coming up from your tank.

A Clog in the Toilet or Black Tank

A clogged toilet or black water tank reduces waste flow by keeping very close to the toilet bowl. While the stoppage might not immediately lead to a water backflow, it could cause a foul stench to leak into the RV.

Clogs often happen when you flush the wrong stuff down your RV toilet. This ranges from anything other than RV toilet paper, poop, pee, or vomit. 

Using too little water or a lot of toilet paper could also clog your RV. And yes, don’t use household toilet paper. You need softer and easy to break down RV paper to avoid clogging your plumbing.

We did a comprehensive guide on how to unclog an RV toilet. You can check it out for more insight into dealing with blockages.

The Weather is Too Hot

The bacteria in your waste tanks thrive in warmer temperatures. Additionally, the high temperature expands generated gas, giving it more pressure. This is why RV toilets smell worse in hot weather.

This combination makes it easier for more foul gas to escape into your RV whenever you flush the toilet.

You can mitigate such situations in summer by:

  • Emptying your wastewater tanks often
  • Using odor-treating cleaners when flushing and cleaning your blackwater tank
  • Parking your RV under the shade to keep temperatures low
  • Keep your toilet, bathroom, and kitchen very clean

Turning on Your Vent Fan Too Soon

Bathroom and toilet vents are a great way to control moisture and bad smell in tight confines. However, in the case of the toilet, turning the fan on too soon could make things worse.

Exhaust fans vent a room by sucking out stale air and creating negative pressure that pulls fresh air through the doors or any other opening.

If you turn on the ceiling fan as soon as you get into the toilet, the negative pressure could also suck in some of the sewer smell from the black water tank as soon as you flush.

The best way is to wait until you flush the toilet to turn on the vent fan. It’s the perfect time to get rid of any smell without adding more into the equation.

How to Keep RV Toilet Odor Smell in Check

Apart from fixing the above problems and keeping your toilet and black water tank very clean, you can do things better by trying the following three tricks.

Empty and Flush your Blackwater Tank More Often

Don’t wait until your black water tank is full before emptying it – especially in summer. Emptying it and flushing it with clean water frequently reduces how much active bacteria is in the tank. It also reduces the chances of blockages.

Install a Vent Fan and Some air Fresheners

While you can reduce the smell after using an RV toilet, you can’t get rid of it completely. Masking and venting the remaining percentage is the only way to a stench-free motorhome. This is very important if you share the space with other people.

  • Install a ceiling vent fan and use it after flushing the toilet
  • Get a room freshener to spray in the toilet room after doing your business

Some people go a step further and get RV tank deodorizes that go into the RV tank. They have a strong better fragrance that masks the sewer smell. While this might work, it makes it harder to know when your tank stinks more than it should.

The chemicals could also harm the bacteria in the waste tank reducing waste breakdown and encouraging clumping that will cause blockages.

Using Bacteria and Enzymes to Compete With Odor Producing Bacteria

Replacing the anaerobic bacteria that create a foul smell in your waste tank with enzymes and aerobic bacteria that break down waste without much of the foul smell is a good way out.

This will keep the waste breakdown process going, reducing the chances of blocking your RV plumbing and the waste tank.

Can I Use Caustic Chemicals to Kill All the Bacteria?

While caustic chemicals in most waste tank treatment chemicals get rid of the stench, they kill all the bacteria in the waste. This stops any decomposition and foul gas production.

Consequently, the waste forms clumps that will clog your RV tank. Moreover, the chemicals will also wreak havoc in the sewer system you finally dump into.

Some states and jurisdictions have even outlawed such chemicals in treating sewage. Look for alternatives and ensure that your black tank treatment never kills bacteria.

A passive approach like getting the perfect toilet seal, ensuring the vent pipes are open, and cleaning your waste tank with clean water should be good enough.

Oscar

In his spare time, Oscar loves tinkering with electronics. Solar panels, wiring, old TVs and sometimes DIY powerwalls. When he is not busy trying not to electrocute himself, you can find him in the garden tending to his vegetables and chickens.

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