black tank not venting?
We have a 2020 high end 5th wheel and also own a 2019 motorhome, and have owned many other coaches. This is the first time we have had this problem and I suspect a black tank venting issue but I welc...
Forum Discussion
It isn't clear to my why, even if the vent pipe is inserted 1/3 the way down into the black tank, why there would be pressure built up. It isn't a sealed system (because of the vent...even if the tube is submerged) so there shouldn't be pressure. Yes, the toilet might burp a bit, but not actual pressure.
Question: Does the smell start happening after it goes over 2/3rds full AND you are flushing the toilet (ie. toilet line open directly to the black tank)? Or does the smell just start showing up in the bathroom and the RV in general once your tank is 2/3rd full? If it is just starting to show up in general (not while flushing) then it seems like there is some other problem. The black tank is supposed to effectively be a closed system (except for the roof vent). That means there shouldn't be any smell while the "stuff" just sits there in the tank. Your toilet itself has a valve/seal and a water barrier so the smell shouldn't be coming from there. Shouldn't matter if it is 1/3rd full, 2/3rd full, or 100% full.
This may or may not be helpful....
Recently, I had a crack/leak on my black waste tank where the 3" pipe from the toilet connected to the top of the tank. That also meant "smell" could leak out anytime there was "stuff" in the black waste tank. Since that connection is somewhat exposed to the floor/underside/plumbing of the RV, I could smell it. ESPECIALLY when driving as the wind (from driving) would swirl around underneath the RV and push the smelly air up into the plumbing connections area/etc which happened to be underneath the kitchen sink/cabinets. The only solution for me was to drop the black waste tank, fix and reseal everything, and then install it back in place. Here's a link to that job in case it is helpful.
https://www.rv.net/forum/index.cfm/fuseaction/thread/tid/30326133.cfm
If you go to post #10 you will see the complete job with pictures. It Also shows you what the black vent pipe looks like (for my rig) and might give you ideas.
On my 2015 Thor Majestic 28a, my black vent pipe was installed in a way that there would be NO CHANCE to slide it in/out (seemed to almost be glued in place).
You can test to see if there is a leak at the top connections to your black tank... The first step is to EMPTY your black tank and give it a good flushing. You don't really want to be testing for leaks with poopy water. Then, simply fill it 90% of the way with water with your flush system. Then, turn off your water pump, get a 5 gallon bucket and slowly start to pour water into your black tank through your toilet. Eventually the black waste tank will fill up (you will kind of be able to hear as it is filling to the top). Then continue a bit more and you will fill the 3" waste line that is going from your toilet to your black waste tank. Then you can even fill up to your actual toilet about 5-10% full (keeping your foot on the flush pedal). If you have no leaks, the water will just sit there and not go down at all. If you have a leak, you will notice that the water level in your toilet starts to go down and the water down in your toilet waste line will go down also. Presumably, you should see a puddle of water underneath your RV if you have a leak (...the water has to go somewhere, right?). If you have a leak in your black waste tank/plumbing, that could be what is causing your smell.
Sorry you are going through this...not a fun problem. Keep us posted.
It just occurred to me that you could have BOTH problems....the tank vent could be 1/3rd into the tank AND you could have a small leak in the connections to the black tank (either the vent, or the toilet, or maybe your bathroom sink). If it is a small leak, then perhaps when the tank is less than 2/3rds full MOST of the smelly air vents out the vent pipe to the roof. But when it is more than 2/3rds full, maybe the vent pipe is submerged and now the stinky air cannot go up the vent pipe and finds its way through a leaky black tank connection (and then the smell drifts up into your RV).
Good luck!
Chris
Question: Does the smell start happening after it goes over 2/3rds full AND you are flushing the toilet (ie. toilet line open directly to the black tank)? Or does the smell just start showing up in the bathroom and the RV in general once your tank is 2/3rd full? If it is just starting to show up in general (not while flushing) then it seems like there is some other problem. The black tank is supposed to effectively be a closed system (except for the roof vent). That means there shouldn't be any smell while the "stuff" just sits there in the tank. Your toilet itself has a valve/seal and a water barrier so the smell shouldn't be coming from there. Shouldn't matter if it is 1/3rd full, 2/3rd full, or 100% full.
This may or may not be helpful....
Recently, I had a crack/leak on my black waste tank where the 3" pipe from the toilet connected to the top of the tank. That also meant "smell" could leak out anytime there was "stuff" in the black waste tank. Since that connection is somewhat exposed to the floor/underside/plumbing of the RV, I could smell it. ESPECIALLY when driving as the wind (from driving) would swirl around underneath the RV and push the smelly air up into the plumbing connections area/etc which happened to be underneath the kitchen sink/cabinets. The only solution for me was to drop the black waste tank, fix and reseal everything, and then install it back in place. Here's a link to that job in case it is helpful.
https://www.rv.net/forum/index.cfm/fuseaction/thread/tid/30326133.cfm
If you go to post #10 you will see the complete job with pictures. It Also shows you what the black vent pipe looks like (for my rig) and might give you ideas.
On my 2015 Thor Majestic 28a, my black vent pipe was installed in a way that there would be NO CHANCE to slide it in/out (seemed to almost be glued in place).
You can test to see if there is a leak at the top connections to your black tank... The first step is to EMPTY your black tank and give it a good flushing. You don't really want to be testing for leaks with poopy water. Then, simply fill it 90% of the way with water with your flush system. Then, turn off your water pump, get a 5 gallon bucket and slowly start to pour water into your black tank through your toilet. Eventually the black waste tank will fill up (you will kind of be able to hear as it is filling to the top). Then continue a bit more and you will fill the 3" waste line that is going from your toilet to your black waste tank. Then you can even fill up to your actual toilet about 5-10% full (keeping your foot on the flush pedal). If you have no leaks, the water will just sit there and not go down at all. If you have a leak, you will notice that the water level in your toilet starts to go down and the water down in your toilet waste line will go down also. Presumably, you should see a puddle of water underneath your RV if you have a leak (...the water has to go somewhere, right?). If you have a leak in your black waste tank/plumbing, that could be what is causing your smell.
Sorry you are going through this...not a fun problem. Keep us posted.
It just occurred to me that you could have BOTH problems....the tank vent could be 1/3rd into the tank AND you could have a small leak in the connections to the black tank (either the vent, or the toilet, or maybe your bathroom sink). If it is a small leak, then perhaps when the tank is less than 2/3rds full MOST of the smelly air vents out the vent pipe to the roof. But when it is more than 2/3rds full, maybe the vent pipe is submerged and now the stinky air cannot go up the vent pipe and finds its way through a leaky black tank connection (and then the smell drifts up into your RV).
Good luck!
Chris
