Black Tank Odor

[wagal64]

We have the 2016 3911 FB. It has the bath and a half. Our problem is with the half bath. Even when it was new within a couple of days after draining and flushing the odor coming from the tank when flushing will knock you down. I'm wondering if there is a ventilation problem. The unit has two gray tanks and two black tanks, but I don't know how the roof vents are configured to the tanks. We have no problem with the main bath toilet. The tanks are completely flushed using the tank flush, back flush through the outlet pipe and even occasionally using a spray wand inserted through the toilet. I always add plenty of fresh water to tank after flushing before use. I have even used the orange additive although it was never needed in any of our other rv's. Nothing works. Any suggestions would be appreciated.

[andylparish]

We use lots of water to flush and a cap full of liquid calgon after each dump in our 2015 3910FB.

[jimcol]

I had the same issue for the first time in eleven years,when I brought the unit out of winter storage. It was RANK. Took a hose up on the roof and inserted it in the black tank vent. Let it run for about 5 minutes at full force. Never felt a restriction as I lowered the hose down the pipe but after the flush the odor disappeared. Can only assume I flushed an obstruction out of the vent.

[WaltBennett]

X2 on the vent probably being obstructed. I wouldn't stick a hose with water down it until you've made certain it's even hooked up though. Some strange things happen at the factory on occasion.

[DQDick]

Sounds like the vent to me also.

[wagal64]

I'm thinking ventilation is the most likely culprit also. I'm not sure how it can be checked out without taking a lot of stuff loose. With most products you can obtain a schematic to see how things are laid out, but not with a Rv. You can't even get an owners manual that is specific to your model, just a generic one that is usually very little help. I can always take it in to the dealer to be checked out, but I am trying to avoid this. We are full-timers with four little dogs and a cat and it is a major operation to leave it in the shop.

[andylparish]

We use lots of water to flush and a cap full of liquid calgon after each dump.

[BB_TX]

I would expect there to be a sewer vent cap directly above the half bath. You might remove the cap and run a snake down the vent pipe first just to make sure it goes all the way down to the tank with no obstructions. You should get a little "stuff" on the end of the snake if it does. Then you could put a hose down it and flush it well as noted above.

[1retired06]

We have a 2015 3910 with the same setup. Have not had a problem with the half bath. Agree with the recommendations above, if you have flushed the tank well, I would look at the vent.

[twindman]

A question for anyone - Are the vents on the roof those round plastic caps that are about 8 inches across? One of mine broke from too much sun and I replaced it, but don't know what they are for.
Thanks.

[rohrmann]

Those mushroom vents are attic vents. The sewer vents are smaller.

[waynemoore]

8" across that's a vent for the living area. To vent the living area. I have 3 one in the potty area one in the hall by the shower and the fantastic fan for the rest of the rig.

[jcurtis934]

Assuming you have the same cheap tank vents that came on mine, there is a screw beneath some silicone on the top of the vent. Remove and you can take it off. It should smell up there...if not...beware. the only way I know to easily id a vent to a tank is dump coolaid powder down the vent and see if the color comes out the other end. The one thing I know is that one bottle of 'awesome' into a tank with some water and then driven to the next campground, will clean the heck out of a tank. John