The question I really didnt want to ask

[Zman65]

Hi All,

 

We just finished our 4th weekend adventure so still very new to this. On this past trip we stayed 3 nights and toward the end when we would flush the toilet and an unpleasant smell  came from the black tank. I realize why there is a smell but is there anything that can be added to keep smell down until next clean-out at dump site? We do put the additive in after clean out and have no problems when RV not in use. We were told it is best to keep dump valve closed until ready to do clean out instead of leaving it open.

 

Thx for any tips and again excuse the question I didn't want to ask 😮

[Dutch_12078]

There are two key rules for RV toilet flushing. Use plenty of water and never turn the vent fan on. If needed, the fan can be turned on after flushing is completed. Many of us use no chemical additives, just lots of water, and get along fine with virtually no odor problems.

[NDBirdman]

If your slinky is connected and you leave your black tank dump valve open, your getting gas from the sewer system.  Also, for a black tank to operate properly and not stink, there needs to be water in all the time.  If not, any solids deposit'd will splat down hard into the tank and become part of the tank, so to speak and hard to clean out.  Having water/solid mix allows the bacteria to work and break down what you deposit there.  I clean mine out before parking for the winter and leave it empty.  BEFORE I use it in the spring, I dump in 5 gallons of used water from washing dishes, etc.  As a minimum, clean fresh water.  I stopped using those magic pellets/crystals, etc after my first couple trips, no need for them IMHO.

Edited July 15, 2020 by NDBirdman

[NDBirdman]

Also, when you dump on your way out, close valve before it is totally empty.  Leave some sewage, ie, poop eating bacteria in there to start the next deposit's occurrence.  When I dump, I always dump the black tank first and shut off before it goes empty, then open the gray water tanks.  It will flush out the hose so it does not smell as bad next time you use it.

[Darryl&Rita]

When it smells, ours is ready to dump.

[Kirk W]

1 hour ago, Zman65 said:

On this past trip we stayed 3 nights and toward the end when we would flush the toilet and an unpleasant smell  came from the black tank.

There are several possible reasons that this could happen, with the most common as Dutch mentions, if you have your bathroom exhaust fan running when you flush you will cause the odor to come from the tank into the bathroom and nothing you put into it will change that. It is because the fan blowing outward creates a slightly lower air pressure in the room than outside and the black tank has a vent that goes up through the RV roof to the outside so it is at outside air pressure and the vent running will pull air in through the tank and open flush valve. Either turn the fin off or turn it to push air into the bathroom before you flush. An RV toilet is very different than one at home and that large throat opens directly into the waste tank where you have been putting poop for several days. 

There is also a chance that your tank vent was plugged and causing that but that isn't common. Occasionally bugs will build nests in that line and plug it, but I have only seen that one time in more than 40 years of RV experience and that was not my RV. It is also possible that wind in the wrong direction blowing over the vent, can cause that to happen. Below are pictures, first of the standard vent cap most typically found on an RV and the second one is a picture of one that turns with the wind to cause a slight vacuum in the tank and helps to prevent the odor issue. 

                          

[sandsys]

You implied you left your black tank valve open. That is NOT a good idea. It leaves solids in the tank which can create the dreaded mountain and cause the smell. The only way to get rid of that is to add lots of water and let it sit as long as you can before flushing. Repeat that process until all the solids dissolve and the accompanying smell goes away. Always leave your black tank valve closed until the tank is at least half full so as to get a good flow when you dump.

Linda Sand

[Zman65]

2 hours ago, sandsys said:

You implied you left your black tank valve open. That is NOT a good idea. It leaves solids in the tank which can create the dreaded mountain and cause the smell. The only way to get rid of that is to add lots of water and let it sit as long as you can before flushing. Repeat that process until all the solids dissolve and the accompanying smell goes away. Always leave your black tank valve closed until the tank is at least half full so as to get a good flow when you dump.

Linda Sand

Hi Linda. 
I thought I indicated we kept closed until time to leave/washout but if not that is what we have done. 
 

thank you all for help. Sounds like main culprit could be exhaust fan running.  Next time we will keep it off. 
 

thx again 

Edited July 15, 2020 by Zman65

[sandsys]

9 hours ago, Zman65 said:

We were told it is best to keep dump valve closed until ready to do clean out instead of leaving it open.

I understood this to mean you were leaving it open until you were told otherwise. Sorry about the confusion.

Linda