I posted a while back about a venting problem we had with our 5th wheel that is. Sing lived in while parked indoors. (https://www.rv.net/forum/index.cfm/fuseaction/thread/tid/30096797/gotomsg/30097053.cfm#30097053)I capped all three tank vents, black and two grays, with dryer vent hose and ran them outside the building. This solved our smell inside the building but outside the trailer problem. However, lately we are experiencing a bad - and I mean REAL bad stink every time we flush on the inside of the trailer. I have been draining and flushing the black water tank twice a week but this doesn’t seem to help. I am hesitant to use strong chemical deodorizers because the trailer is dumping through a future toilet flange to our septic tank and drain field. What do I do? The wife is ready to move out, it’s that bad.

I put a product like Happy Camper in both the black and the gray tanks and that stops the inside odor. They are septic friendly.You may call me if you wish.

Just muy guess! You hooked up 4" dryer vent piping to the top of each vent stack. Did you remove the vent stack cover? Are you venting the dryer hose straight up, no bends or angles? If its a long run you may want to get some type of inline fan to help draw the oder out. When you empty the black tank are you rinsing the tank also? Maybe you are not allowing the black tank to fill enough before emptying. Depending on the size of the tank twice a week may be to often. I would keep flushing the tank until clean water comes out.

Link to Previous PostI agree with craig7h, consider using an inline fan to vent the tank.Possibly when you flush, the relatively cooler air in the vent line is falling back into the black tank and pushing out of the toilet.

For the past 20 years we have used Thetford deodorizer in our black water tank. One treatment per tank.Although many will tell you that it's not necessary, I would strongly disagree. In the 20 years of RVing we have never had an issue with odors, tank clogs, or any other horror stories you hear about related to black water tanks.

Add more water. The only way for odors to go back into your trailer is through the toilet, which means you are leaving the flap open too long or are not adding water to cover the flap.

Toilet Smells Horrific When Flushing | Good Sam Community

Jebby14
Explorer
Aug 25, 2020
power vent those dryer ducts. id bet you have more pressure in them than the washroom so the stank is equalizing into the camper instead of out.
winesalot
Explorer
Aug 25, 2020
Thanks for all the great replies, I appreciate your taking time to help me out. Here are my responses:

No bleach or other chemicals for me. The septic system we installed for our building was extremely expensive and I am not going to mess with that biology.

Moving the trailer out of the building is not an option right now.

Vent is definitely not blocked.

I have thin vinyl dryer type hose connected to all three tank vents and they are tee'd together to one vent line exiting the building. There are definitely lots of bends and it does not go straight up.

This morning I installed an inline vent van in the common line from all three vents. Let's see if that helps.

Cheers!!!
lakeside013104
Explorer
Aug 25, 2020
Cummins12V98 wrote:
Too funny, I have heard this "Vent could be BLOCKED" theory for so many years but NOT one example of it really happening.

Toilet WILL allow odor to escape when a fan is running plain and simple.

Sounds simple enough. Remember, the 'grey' water tank can smell as bad or worse than the black water tank. You may be doing everything fine to vent the black tank and flush it properly, but forgetting the grey water tank could be problematic as far as smells go.

Good luck & keep us posted.

Lakeside
Bowti
Explorer
Aug 24, 2020
Exhaust venting needs to be done correctly to get it to draw upwards and through the roof and away from occupants. Incorrect modifications if not done correctly are going to cause big problems. Also, it is not unheard of to be restricted in some manner, especially if modified.
An explanation of how he modified the venting might give insight to his problem, length, size of pipe, and angle?
cummins2014
Explorer
Aug 24, 2020
Those exhaust fans plain ,and simple won't cause that sort of odor, that does sound like venting gone haywire. Sure if you stand there with the toilet flushing for too long you are going to pull some odor up, but normally that fan can run ,and flush fairly quick its going to be okay. Sure sometimes you will get a faint odor, but nothing like the OP is describing.
Mountaintrails
Explorer
Aug 24, 2020
Hello, are you dumping directly into the future house septic system? The toilet flange goes straight to the septic tank with no P trap system. I will bet you are getting the septic tank venting up into your rv. I would diconnect the sewer hose from the rv for a while and see if the smell goes away.
Good luck
time2roll
Nomad
Aug 23, 2020
I agree with DW. Move the RV out of the enclosure.
campigloo
Explorer
Aug 23, 2020
Cummins12V98 wrote:
Too funny, I have heard this "Vent could be BLOCKED" theory for so many years but NOT one example of it really happening.

Toilet WILL allow odor to escape when a fan is running plain and simple.

Yeah real funny Cummins. The water hose thing worked for me!
Cummins12V98
Explorer III
Aug 23, 2020
Too funny, I have heard this "Vent could be BLOCKED" theory for so many years but NOT one example of it really happening.

Toilet WILL allow odor to escape when a fan is running plain and simple.
Bowti
Explorer
Aug 22, 2020
Think of what you have done by extending the vent with the extended tubing. You now have fresh air coming in from outside and exiting from your tank into your RV every time you flush your toilet. Venting needs to go almost straight up and threw the roof. Listen to others and either reroute the venting or get a inline fan to get a positive flow outside.