Black tank odor in RV when dumping

[NCKZ_Camper]

Went on maiden trip with our new KZ Spree 329 IK. We were in full hook up site. On departure our black tank was 3/4 and grey tanks 3/4 full. I've RVed for a number of years (being our 3rd RV) and think I know how to properly dump. Opened black tank valve dumped great, then closed valve when empty, opened grey dumped fine and closed valve. Proceeded to hook up factory installed black tank flush system. Opened black tank valve and turned on water hose to flush line.

Wife immediately yelled there in bad sewer odor in our travel trailer. I tunrned off water to black tank flush and went inside and boy it was a horrible smell. Confirmed on panel all tanks read empty too.

No leaks anywhere, no evidence of any problems, but highly unsusual for the smell to be so pronounced when using the factory installed flush.

Any advice out there on why this happened?

[down_home]

Yep! RVs are pretty tight units and a little vacuum will draw sewer gasses from sewer system if open and no water in traps or the shower. flush the toilet and it comes right in big time.

[dan-nickie]

popeyemth wrote:

hawkeye-08 wrote:

dan-nickie wrote:
Did you have any fantastic or ceiling fans running with no windows open.
That's what happened to us a few days ago.

While the dump vlave was open for a few minutes, the fan sucked the smell up through the sinks.

Curious how you could get smell through sinks.. unless your traps are dry..

Sometimes the vacuum breaker sticks and the outrush of grey water will suck (via the vacuum created ) the traps dry.
Air has to replace the gray water and if things don't work right that air will come from the sink or shower trap.

Not sure I can satisfy your curiosity, but here is what happened to us a few days ago.

1. We had the Grey tank valve open as we were doing laundry in the coach.
2. That evening, we turned on the 'kitchen' fantastic fan and opened some windows to keep us cool during the night.
3. Next morning it was cold inside so DW closed all the windows (but left the fantastic fan on).
4. Soon the whole RV smelled like sewer.

After some investigating, we closed the Grey tank valve and turned off the fan. Then the smell started to susice.

I would assume the fantastic fan had been drawing the odor through the sinks since the gray tank valve was open.
****

Since the OP said they left the black tank valve open at least for a while as they were flushing the tanks, I thought maybe a fan was pulling odors in while the valve was open if they had one turned on.

[NCKZ_Camper]

fpresto wrote:
My money is on the bathroom vent being open. In almost all cases the black tank vent on the roof is close to the bathroom vent. If you have any cross ventilation the gasses are pulled right inside. I often open the bathroom vent and run the Fantastic Fan blowing out on the other end to create flow through ventilation. It didn't take me long to learn to close the bathroom vent while dumping the tanks.

After reading posts likely the vent being open was the problem. Funny in all the years RVing I never had this to happen. I remember when we broke camp the atmosphere was heavy/humid & the vent was open so likely that was it. I'll close the vent from now on!

[fpresto]

My money is on the bathroom vent being open. In almost all cases the black tank vent on the roof is close to the bathroom vent. If you have any cross ventilation the gasses are pulled right inside. I often open the bathroom vent and run the Fantastic Fan blowing out on the other end to create flow through ventilation. It didn't take me long to learn to close the bathroom vent while dumping the tanks.

[dougrainer]

NCKZ Camper wrote:
I do think the roof vent in the bath was open, but not sure if fan was running. I did notice this morn when I checked that both my kitchen sink and bath sink have venting under the sinks and not through the roof! Maybe the pressure forced some gas from under the sink vents?!?

Those are NOT the tank vents. They are mechanical plumbing vents. The gray and black are separate tanks, BUT, on some RV's they use the same roof top vent pipe. See if you have 1 or 2 roof top vent pipes. Doug

[popeyemth]

We get odors if the bath vent is open.

[NCKZ_Camper]

I do think the roof vent in the bath was open, but not sure if fan was running. I did notice this morn when I checked that both my kitchen sink and bath sink have venting under the sinks and not through the roof! Maybe the pressure forced some gas from under the sink vents?!?

[popeyemth]

hawkeye-08 wrote:

dan-nickie wrote:
Did you have any fantastic or ceiling fans running with no windows open.
That's what happened to us a few days ago.

While the dump vlave was open for a few minutes, the fan sucked the smell up through the sinks.

Curious how you could get smell through sinks.. unless your traps are dry..

Sometimes the vacuum breaker sticks and the outrush of grey water will suck (via the vacuum created ) the traps dry.
Air has to replace the gray water and if things don't work right that air will come from the sink or shower trap.

[dougrainer]

1. When flushing with a Black tank Flush, you WILL get any tank odor out the top roof sewer vent. The top vent cap may be on too tight and not allowing the tank to vent properly or the abs up pipe is not sealed where it goes thru the roof cavity.
2. It is possible that the back flush check valve does NOT leak water but may leak gas, but I doubt it as there is water constantly going thru it, so no gas can come back up.
3. Black tank odor is RARE IF you use chemical. Using chemical not only breaks down the solids but makes the tank smell much nicer and should not have that outhouse smell.
4. Dump your tanks and flush. put a qt of pine sol in the black tank. Flush your black tank with the flush system. See if you get the pine sol smell in the RV. If NOT, then your odor is from the gray tank. Doug

[hawkeye-08]

dan-nickie wrote:
Did you have any fantastic or ceiling fans running with no windows open.
That's what happened to us a few days ago.

While the dump vlave was open for a few minutes, the fan sucked the smell up through the sinks.

Curious how you could get smell through sinks.. unless your traps are dry..

[dan-nickie]

Did you have any fantastic or ceiling fans running with no windows open.
That's what happened to us a few days ago.

While the dump vlave was open for a few minutes, the fan sucked the smell up through the sinks.

[2oldman]

I think it's normal. After 12 years of this, I find it's hard to escape odor.

[NCKZ_Camper]

HappyKayakers wrote:
Maybe your backflow preventer blew off the line. Mine was not installed properly from the factory but didn't notice until there was water pouring out of the underbelly.

Checked the backflow preventer also as it is on a closet and very accessable. No leaks there. There is only the odor issue.

[HappyKayakers]

Maybe your backflow preventer blew off the line. Mine was not installed properly from the factory but didn't notice until there was water pouring out of the underbelly.