Black tank odor - switch to macerating toilet?

[richard5933]

Just to clarify that when I said we only have problems when the bus is on the road and in motion I was talking about if someone flushed while we were moving.

No problems with odor while on the road unless the toilet was flushed, then those few seconds allowed odor to be sucked into the bus.

[Scott & Heather]

Don,

1.28 gallons per flush...we have four people living in our bus. That's four flushes first thing in the morning, and several sets of those throughout the day. If each of us only flushed three times a day (and I'm telling you, we flush more than that) the 100 gallon tank would only last around 6 days. That's not enough for us when we are traveling heavily or boondocking in a parking lot. And in real life practice the tank only lasted about 4 days. Just not enough. And chessie, there ain't no house toilet that flushes only a quart or two. 1.28 gal is The minimum. Rv toilets actually do flush only a quart per flush. Literally 1/5th what a house toilet flushes.

[chessie4905]

Maybe I'm  a quart low, I haven't measured it. I know it uses far less to flush than any toilet I ever used. Your situation is a little more elevated than normal for most rv owners; some could probably use a low flow household toilet, but, if a Job Johnny can have that seat hole wide open with no odor in the enclosure, then it is worth checking out. They do use a 3 inch vent though. Since moving RV's have various airflow while in motion,  a fan vent in ceiling of bathroom on while travelling is probably one of the easiest ways to deal with odor issues.

[belfert]

I find on my bus that having the bathroom vent fan on when flushing draws in even more odors when the flush valve is open to empty the bowl.

[dtcerrato]

In some (most) cases a fan vent on while toilet flushing still won't overcome the ambient vaccume that exists in most busses while going down the hwy, especially if the drivers window is open! We just grin and bare it - it's a very fast passing event... 

[belfert]

The boat peeps have an expert.

"The Headmistress" Peggie Hall has a book on these matters.

https://www.amazon.ca/New-Get-Rid-Boat-Odors-ebook/dp/B01BW2ZSTW

Basically, lack of oxygen is what makes bad stink. Proper venting is EVERYTHING.

I am about two thirds of the way through the book.  One of the big takeaways I got from the section on venting is the recommendation to only go horizontal with the vent and not to go over five feet with three feet even better.

Is bacteria really going to take care of the smell if my tank is getting up to 10 deposits of #2 per day?

[richard5933]

I am about two thirds of the way through the book.  One of the big takeaways I got from the section on venting is the recommendation to only go horizontal with the vent and not to go over five feet with three feet even better.

Is bacteria really going to take care of the smell if my tank is getting up to 10 deposits of #2 per day?

Actually, I've been reading that much of the odor in the black tank actually comes from the urine in the tank, not the solid materials. Makes sense, as anyone walking into a campground restroom with non-functioning urinals can attest to.

I think separating out the urine from the solids is how composting toilets can function without odor problems.

When we had horses, the smell emanating form the manure pile was always less troublesome than the urine which would seep under the rubber mats and turn rancid.

[chessie4905]

Maybe better sealing of the bathroom door and enclosure is a thought. Maybe the smell you have is coming up through the mouse holes in the floor from your non roof vent. If yout toilet has a good water seal, sink and shower traps are working, where is the odor coming from? Is the water seal bubbling? This has been an ongoing issue for years for scores of bus nuts.

[belfert]

The odor is almost entirely from when the toilet is flushed.  There will be a terrible stink when someone flushes the toilet.

[buswarrior]

Multiple little things adding up?

The drop from the toilet shouldn't be the highest opening in the tank, the vents should be. How far do each protrude into the tank top?

The gases will COLLECT up high in the drop from the toilet and whoosh up into the coach when it gets opened.

The vents should be as flush with the inside top surface of the tank as possible, so the gases go there and leave continuously, not storing in the toilet drop.

The vent(s) have to be big enough and straight enough that there actually is air flow.

Is the end of the tank vent in a high pressure area, or unwittingly catching the wind, instead of shedding gases to the passing wind?

Underbody cavities, who knows whether any particular one, or area, on whichever coach, with whatever fenders, might happen to be a high pressure area?

While underway, opening a vent or window only makes the suction pulling the odours into the coach stronger.
It may disperse the odour faster afterward, but it triggered the gulp of stink in the first place.

Re: horizontal runs.
Buses have the freedom to go vertical. Boat writing focuses hard on the word "horizontal" because the vent is going exclusively out a fitting in the side of the hull, below the edge of the deck. Many manufacturers and peeps retrofitting, leave loops or aim then conveniently down, without realizing that airflow is being hindered.)

Lots of variables to have accidentally have a stinky experience.

Happy coaching!
Buswarrior

[sledhead]

no free lunch with any toilet ( stink any way ) I have a headhunter water jet toilet similar to below and there is zero smell when you flush  but it uses water to do that . the only bad smell is from the person making the stink . the water jet blasts the "stuff " as it is going out of the toilet  like a pressure washer
 
sure glad that I did not pay for it

https://www.headhunterinc.com/product/espresso/


dave

[Jim Blackwood]

Actually if you research toilet odors you find that most of the stinky gases are heavier than air. How about that, huh? So what is actually happening in your black tank is that the gases are accumulating, building up, and pushing the air out the top of the tank vent so that now you have a stack of stinky gas just waiting on you to open the toilet valve so they can drop down into your bathroom. If you're moving, have a window cracked, and run the bathroom vent fan so much the better! (worse) Maybe this is why some of our guys with low vents are getting by with it. But that does mean stink around the wheel well.

The solution is to get those stinky gases replaced with fresh air, send them up high and disperse them in the wind like they should be, but this takes energy. Maybe not a whole lot, but at least enough to scavenge the black tank. That means a minimum of two vents, one of which is fitted with some means of generating a slight suction. Could be a bilge fan connected to the bathroom light switch. Could be one of those fancy wind powered vent caps. Could be something else entirely. Could be run on compressed air for instance. Could be solar. But the key is, it has to scavenge the tank effectively. That's not really asking that much, it could be constant, intermittent, or on-demand. Could be high flow or low flow. But the bottom line is, if you blow those heavier than air gases out of the holding tank before you open the valve there will be no stink to climb up the toilet into your bathroom. And you have the side benefit of promoting aerobic bacteria in the tank, further reducing the stink. Win-win.

Jim

[Geoff]

I have a special adapter that goes on the top of roof that vents to suck air out of the black tank while driving.

[Jim Blackwood]

Geoff, add a second vent line to let fresh air into the tank and you should be able to further improve your system. Try to go for the opposite corner of the tank.

Jim

[chessie4905]

Maybe a  constant small flame at the vent pipe outlet. Should look good at night.