Check if your roof vent for the black tank is clogged. If you have a plumbing snake, you can run it down the pipe from the roof. You might need something like this for a vent cap:

 

This is a Cyclone Sewer Vent and you can get it from Camping World, Amazon, etc.

Do you only get the smell when flushing or is it present in the RV when the valve is closed after the 5 day period? I know some people say they don't smell but in reality, you have a box where you are storing.........and when it sits, especially the warmer it is........... I also think the more TP you use, the worse the problem and I think even different types of TP (we never used the expensive RV type) make a difference in the smell and the ability to get the tank clean(ish). Another issue is to make sure you don't mix and match chemicals putting in stuff for the toilet and then cleaning with yet something else and sending it into the mix.

found a solar powered fan that just replaces the cap.. anyone use these?
www.adventurerv.net/ultra-fab-mini-solar-plumbing-vent-p-22616.html

I would check the vent first. Or how long has it been since the gasket between the flange and the toilet was replaced. They get hard and allow smells to escape which may show up during flushing due to the change in pressure when the flap opens.

I use Thetford Deoderizer Powder with enzymes....it has a pine fresh smell

We sit for two weeks without dumping and no smell.

Try it if your vent isn't clogged.

The Cyclone vent is the way to go. I have one for each vent and they work great even when sitting still. The Cyclone rotates with the breeze and draws "gases" from the vent. Another thought is the amount of water. Every 3 weeks or so when I dump the tank I add at least 2 very full toilet bowls full of water, 5 to 10 gal of water to start off with. Then use water pretty liberally when flushing. Before you install the Cyclone use a snake to be sure the vent pipe is clear. I have rarely put any chemicals in the tank and it's not a problem. Good luck.

Bruce

Steve - we have the same problem with our DRV. I thought it was also just the way of the rig telling us it was time to dump (which is also about every 4-5 days). It does seem to get better after we dump.

These are sealed systems, if things are working properly the amount of content in the Black Tank should not affect the smell one way or another...The tanks should be dumped ONLY when full, and should not get more smelly as the tank fills.... their are different types of toilets that also factor in, we have, and still have both Automatic Macerator Tecma Toilets, and manual Foot pedal toilets....with the manual toilet the rubber seal (gasket) must be intact and sound, if not, the seal is compromised and odors will back up.....This is not as big as a factor with the macerator toilet..Lastly not only does the vent have be open, but it has to be plumbed correctly and hooked up...I have read more than one post that people have discovered vents missing, detached, and fallen into the black tank....we added the Cyclone as well and never have any odors....

SnowGypsy wrote:

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OK, so having a vent fan of some sort at the top of the stack sucks air outward once the flush gate opens so that the smell doesn't come up but the fresh air sucked from the "house" goes out the vent? Is that it? We never had one but I was thinking that usually a fan would need air coming in in order to do its job except in the cases where it was just circulating air in an enclosed area.

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 When the valve opens to transfer the content from the bowl to the tank the air is provided....That's why some people complain of odors while flushing if they have the Fantastic fan on, same idea only pulling the odors into the RV with the fantastic fan...

We always wait until the tank burps and we know it is full. As Gene said a full tank will help clear out especially near the valve. After every dump we flush the tank. We always use lot of water. We also use Scott single ply and have never had issues. Check your valve to make sure it is not leaking liquid because even a small leak due to the valve not closing will leave solids which will build up and stink to high heaven!

Steve,

A couple of things for you.  I don't think the amount of time you are sitting in one campground before moving is a problem for the odors.  We've been "static" full-timers for over three years now and have not experienced what you are.

As for flushing, here is my procedure.  I first dump the black tank and watch the clear plastic extension on our sewer line to see that it has quit running.  Then I start the flushing system and let it just flush and empty for about 5 minutes or so.  Then, I close the black tank valve for 2 1/2 minutes and then open the valve for another 2 1/2 minutes.  I consider the two (closed and then open) as one cycle.  All of this is done while the black tank flushing system is running.  As it is emptying the flush water, I again watch the clear plastic extension for debris, including bits of paper.  If there is any, then I do another "cycle" of 2 1/2 minutes closed and 2 1/2 minutes open.  Once I don't get any debris, I close the black tank valve while the flushing water is running and then after about 30 seconds or so, I shut off the water to the flush system.  That allows there to be a bit of water in the tank to help "dissolve" any solids put into the tank before a lot of flushing is done.

Under no circumstances do you want to fill the tank with "flush system" water before dumping again.  It's too "iffy" as to just when your tank is full.  Also, never allow yourself to be distracted by anyone while flushing.  Folks have filled their tanks and toilets before because they got distracted and forgot to turn the water off.

Terry

Also, do not leave a hose attached to the flush system, hooked to a faucet or laying visible.
You go away, the water goes out and some one runs around and turns off all faucets. When the water is back on and clear, someone runs around and turns on all faucets that have hoses attached. Or a maintenance person disconnects your hose to use it, not noting the faucet was turned off, or they see your hose laying there and connect it. When done, they hook you hose up and turn on the faucet. Either way, you come back to a flooded RV. This has happened to multiple RVers through the years.