Help, please! Sewer smell

[Claassen]

Good morning!

I wonder if someone may be able to provide some instruction/ideas for an issue we have been happening recently. My husband and I are relatively new to camper life, so I’m unsure where to start. We are in a 2021 Sprinter 29RL. (not sure if that is necessary information, but here we are.) Anyway, we have noticed within the last week of camping that when we flush the toilet IF the secondary AC in the bedroom is running there is an AWFUL sewer smell. I have read other posts in the forum explaining that the AC only recirculates interior air (which my husband had already told me). If only the main AC is running there is no smell. If no ACs are running there is no smell. The only time we are getting this awful sewer smell is when the upstairs AC is running and we flush the toilet. Also, when this happens the sewer smell is strongest in the bedroom where the secondary AC is. Does anyone have any idea where we need to start? What we need to look at?
Thank you so much!

 

[Mr Lars]

Turn the ac off when using the commode?
Once you get into the routine of doing that, it’s not so bad. In our RV, we need to shut off the ac in the main living area, when using the microwave, otherwise it trips the circuit breaker out on the pedestal, usually when it’s pouring rain.

 

[Claassen]

Turn the ac off when using the commode?
Once you get into the routine of doing that, it’s not so bad. In our RV, we need to shut off the ac in the main living area, when using the microwave, otherwise it trips the circuit breaker out on the pedestal, usually when it’s pouring rain.

Honestly, that's what I did this morning, to verify that when the AC is off it doesn't happen. It's just annoying as my husband leaves early in the morning for work and I usually sleep another hour or so. First world problems, right?!?! lol

 

[Kirk]

First world problems, right?!?! lol

It is a matter of RV design. Since your air conditioner is drawing air from the space around it and discharging it some distance away, that causes a low pressure area at the air inlet and with your bathroom nearby it shares that low pressure area and so will draw air from your black tank through the large opening of the flush valve. In most RVs the toilet flush drops directly into the black tank via a 3" opening. You will have that same experience if you open the top vent in the bathroom and turn on the exhaust fan. You need to remember that in an RV you are putting all of the same things as in your stick house but into a far smaller space. That does create some issues that you would never see in a house.

 

[zulu]

Add a couple of cups of bleach. Fast, always works, and won’t hurt the plumbing.

 

[Claassen]

It is a matter of RV design. Since your air conditioner is drawing air from the space around it and discharging it some distance away, that causes a low pressure area at the air inlet and with your bathroom nearby it shares that low pressure area and so will draw air from your black tank through the large opening of the flush valve. In most RVs the toilet flush drops directly into the black tank via a 3" opening. You will have that same experience if you open the top vent in the bathroom and turn on the exhaust fan. You need to remember that in an RV you are putting all of the same things as in your stick house but into a far smaller space. That does create some issues that you would never see in a house.

It is a matter of RV design. Since your air conditioner is drawing air from the space around it and discharging it some distance away, that causes a low pressure area at the air inlet and with your bathroom nearby it shares that low pressure area and so will draw air from your black tank through the large opening of the flush valve. In most RVs the toilet flush drops directly into the black tank via a 3" opening. You will have that same experience if you open the top vent in the bathroom and turn on the exhaust fan. You need to remember that in an RV you are putting all of the same things as in your stick house but into a far smaller space. That does create some issues that you would never see in a house.

Thank you for your feedback. I have a hard time believing it comes down to trailer design, as it is a recent problem. We camped in the camper for 2 solid months, running the AC and didn’t have the issue. It is something that has happened in the last month. We are in the same spot at the same campground, so it shouldn’t be due to something moving or shifting during transport. That’s why it’s so frustrating.

 

[HueyPilotVN]

Maybe it would help if you did the thing that I have done with all my RVs.

Install a "Venturi Vent". It replaces the regular cap at the top of your roof vent.

The Venturi vent looks like a weather vane and it turns into the wind and creates a vacuum behind it pulling out the exhaust smell on the downwind side and blowing it away from the roof.

Here is a link to see what they look like.

Put one on each vent, usually two or three vents, gray and black water.

Amazon.com

 

[Kirk]

It is something that has happened in the last month.

You are not keeping the black tank dump valve open, are you? That is not a good plan and it could be a source of sewer gas that wasn't always there.

I have a hard time believing it comes down to trailer design, as it is a recent problem.

If so, what are you doing differently?

 

[JudyJB]

You also might want to keep a window open a bit. That will enable the AC to pull air from someplace other than the black tank when you flush. Even opening the bathroom vent, but without the fan on might help.

Another possibility might be a plugged vent stack, but it is unlikely that would happen quickly.

And, yes, these things are not built like a home because they have no traps in the toilet so stuff drops down directly. Another problem is that the toilet is located very close to where people are sleeping or sitting, so odors can be a problem. You might experiment a bit as to what window lr vent you leave open a crack.

 

[Claassen]

You are not keeping the black tank dump valve open, are you? That is not a good plan and it could be a source of sewer gas that wasn't always there.

If so, what are you doing differently?

No. We are definitely keeping the black tank closed. I know that’s a big “no no”. We’re honestly not doing anything differently. That’s why it’s so confusing. It doesn’t make sense that we have changed nothing and are suddenly having this issue. There is no sewer smell at all, except if the upper AC is running and we flush. When we cut the AC off and flush and then immediately cut the ac back on, there’s still no smell.

I just want to say, I know everyone is trying to help, and I appreciate it so much! Like I said we are new to this and acknowledge that there's a lot we don't know. The only thing I can think is that perhaps the vent is clogged. There are squirrels around us, so I don't know if they have stashed something. Could a clogged vent cause an intermittent issue like this? I would think if it was clogged the issue with the smell would be constant, and not just when running the AC and flushing.

 

[Onyrlef]

No. We are definitely keeping the black tank closed. I know that’s a big “no no”. We’re honestly not doing anything differently. That’s why it’s so confusing. It doesn’t make sense that we have changed nothing and are suddenly having this issue. There is no sewer smell at all, except if the upper AC is running and we flush. When we cut the AC off and flush and then immediately cut the ac back on, there’s still no smell.

I just want to say, I know everyone is trying to help, and I appreciate it so much! Like I said we are new to this and acknowledge that there's a lot we don't know. The only thing I can think is that perhaps the vent is clogged. There are squirrels around us, so I don't know if they have stashed something. Could a clogged vent cause an intermittent issue like this? I would think if it was clogged the issue with the smell would be constant, and not just when running the AC and flushing.

Try taping or zip tie a plastic bag over the anti-siphon device under the lavatory and see if the smell persists.

 

[Rene T]

No. We are definitely keeping the black tank closed. I know that’s a big “no no”. We’re honestly not doing anything differently. That’s why it’s so confusing. It doesn’t make sense that we have changed nothing and are suddenly having this issue. There is no sewer smell at all, except if the upper AC is running and we flush. When we cut the AC off and flush and then immediately cut the ac back on, there’s still no smell.

I just want to say, I know everyone is trying to help, and I appreciate it so much! Like I said we are new to this and acknowledge that there's a lot we don't know. The only thing I can think is that perhaps the vent is clogged. There are squirrels around us, so I don't know if they have stashed something. Could a clogged vent cause an intermittent issue like this? I would think if it was clogged the issue with the smell would be constant, and not just when running the AC and flushing.

I’ve been rving for 40+ years and they all had tank vents which pass through the roof. They all had vent caps and there would be no way a squirrel could get down into the pipe. Just get on your roof and see if all vent caps are on

 

[DutchmenSport]

The bottom line is, based on your description, the air conditioner is sucking air UP from your black tank.

Your vent on the roof is not stuck because the air flow is backwards now when the AC is on. Air is being pulled from the outside, down the black tank vent and up through the toilet. If the odors ONLY occur when the AC is running and ONLY when you push the toilet pedel, then THAT IS what's happening.

Bottom line is, your black tank stinks! The simplest solution is to fill the black tank completely full until water actually starts coming up the neck of your toilet. Watch it through the hole in the bottom with the foot valve open. When it's full, dump the black tank.

Now that the tank is flushed at least once very good, add some Dawn Dishwashing liquid to the tank (half a cup or more) and just pour it down. And / or add a half cup of Laundry detergent (liquid if you have it). Now use the toilet as normal. The soaps will help deodorize the tank and help clean it out. You do not need to purchase black tank RV deodorizers. Laundry and Dishwashing products work very, very well.

THAT is what you need to do. Flush the the AC off. Flush out that tank, and then add soap!

Your tank has stuff clinging to the inside, it needs to be flushed out.

 

[roninX]

Definitely start with black tank total flush.

 

[Lou Schneider]

Go up on the roof and check where the black tank vent extends through it. If the hole is oversized or the pipe has dropped down below the roof surface sewer gas can be drawn into the space between the roof and the inside ceiling. If sewer gas can get into this space the air conditioner can distribute it throughout the living area.

 

[zulu]

Go up on the roof and check where the black tank vent extends through it . . .

Then slide under your RV and check for any black tank leaks from road debris, then check each and every plumbing connection, then . . .

Or, just pour some bleach down your toilet.

 

[Kirk]

If sewer gas can be drawn into this space the air conditioner can distribute it throughout the living area.

Lou brings up a good point. if you have not been traveling the vent pipe isn't likely to slip down but it is possible and if you have a ducted air conditioner that becomes more likely.

I think that most experienced RV owners would agree that sometimes things happen that we never do fully understand.

 

[Claassen]

Thanks for all of the ideas and suggestions. Now to figure out what works!

 

[Onyrlef]

Thanks for all of the ideas and suggestions. Now to figure out what works!

The solution to most problems is a process and more often than not the solution is the more obvious or simplest. I'd suggest beginning with the simplest (easiest and most obvious) and working toward the more complex by process of elimination.

 

[Claassen]

The solution to most problems is a process and more often than not the solution is the more obvious or simplest. I'd suggest beginning with the simplest (easiest and most obvious) and working toward the more complex by process of elimination.

Well, if this didn't end up being EXACTLY the case. When I emptied the black tank yesterday, I realized that there was a hole in the emptying hose. I assume there has been a small crack in the hose that was allowing air to escape/enter. A small tree limb had fallen on the hose and there was now a hole. I don't pretend to understand why that would effect having a smell when the air conditioner is on, especially since the black tank is closed, so the hose should be ineffective at that time anyway, but here we are. I purchased a new hose and my husband replaced it yesterday. This has fixed the issue. It doesn't make any sense to me, but it is resolved. I appreciate everyone's help.