How to unplug/unclog a black tank roof vent system

[Aage]

I am suspicious of my venting system for the black tank, and I want to make certain that there is nothing blocking it.

I've done a search and read a bunch about smells, hills, and blockages, and while there are lots of references to a blocked vent potentially being a problem, nowhere could I find a solution.

Oh, great readers, possessors of all and vast knowledgable , how may I be sure that the vent is open and performing its full and proper part in keeping the smellies out of our coach?

Your help is much appreciated in advance.

ps: grumbling to myself that I only replaced the screen and Vulkem caulking on all of them last summer...

[Gene]

Step 1. Purchase beans.
Step 2. Boil beans until soft and add chiles* for flavor and to enhance result.
Step 3. Eat beans and chiles.
Step 4. Wait a few hours.
Step 5. Run yellow caution tape in a wife circle around trailer to protect children and the infirm.
Step 6. Sit on toilet while opening valve.
Step 7. Nature will provide the necessary flatulence to open the vent.

Glad to help.

Gene

*habañero chiles are very strong, may be unavailable in Ontario, but will certainly add to the explosive results.

[r carl]

If you suspect a bird or potatoe in the pipe you can just look down in it with a light. You could also run some water down the pipe to see if it fills up with a couple of gallons, if not its just going into the tank.

[r carl]

Originally Posted by CrawfordGene

Step 1. Purchase beans.
Step 2. Boil beans until soft and add chiles* for flavor and to enhance result.
Step 3. Eat beans and chiles.
Step 4. Wait a few hours.
Step 5. Run yellow caution tape in a wife circle around trailer to protect children and the infirm.
Step 6. Sit on toilet while opening valve.
Step 7. Nature will provide the necessary flatulence to open the vent.

Glad to help.

Gene

*habañero chiles are very strong, may be unavailable in Ontario, but will certainly add to the explosive results.

Flushing a cherry bomb works too.

[Aage]

Originally Posted by CrawfordGene

Step 1. Purchase beans.
Step 2. Boil beans until soft and add chiles* for flavor and to enhance result.
Step 3. Eat beans and chiles.
Step 4. Wait a few hours.
Step 5. Run yellow caution tape in a wife circle around trailer to protect children and the infirm.
Step 6. Sit on toilet while opening valve.
Step 7. Nature will provide the necessary flatulence to open the vent.

Glad to help.

Gene

*habañero chiles are very strong, may be unavailable in Ontario, but will certainly add to the explosive results.

Gene your help is always cherished, then folded and put away neatly. In any event, I tried something along those lines, but the reaction was noted rather vociferously, and it was "suggested" to me that untested experimentation along those lines would not be welcomed in future.

Originally Posted by r carl

If you suspect a bird or potatoe in the pipe you can just look down in it with a light. You could also run some water down the pipe to see if it fills up with a couple of gallons, if not its just going into the tank.

Yes, I had thought of that, but of course the pipe, which can be seen in one of the closets between the rear bathroom and the sleeping quarters, takes a left turn (45°) about half the way down its travel, thus making the light idea unworkable.

I guess that really, I'm hoping for solutions from those who have done this before as to what tools were used and which worked.

For example, a plumber's snake seems a bit of overkill, plus I'm concerned that it could damage the tank.

I'm also not wild about putting any fluids down the pipe either, since I don't see how that would dislodge something that might be stuck in there.

But thanks for your concern and humour so far, I'm still hoping for a magic bullet...

[DaveFL]

I put a snake down from the top when I thought the grey tank was not dumping fast enough, probably same construction for the black tank. Put a hose on full force and it flowed easy, no backup, replaced the valve and it still drains slow, on thinking about it, part of the slow problem is the tank shape, very long and flat compared to the black tank.

[Foiled Again]

Originally Posted by DaveFL

I put a snake down from the top when I thought the grey tank was not dumping fast enough, probably same construction for the black tank. Put a hose on full force and it flowed easy, no backup, replaced the valve and it still drains slow, on thinking about it, part of the slow problem is the tank shape, very long and flat compared to the black tank.

That's what I'd do too.

HOWEVER, there's a big caveat. I've heard that many SOB's just cut a hole in the top of the black tank, drop the pipe on it and put a little seal around it. THEN OVER TIME the vibration from moving the RV causes the pipe to slide down INTO the black tank, eventually getting below the level of the waste and guess what NO more venting except when you flush. Supposedly AIRSTREAM uses a fitting glued to the exhaust pipe to keep it on the top surface of the tank................................. now sure they did that in the good old days, but now?

My personal experience is that I know my vent pipe works. I had a second Fantastic Fan put in my bedroom... right next to the bathroom in the 25 FB. The mothership put in a bi-directional fan, and I LOVE to have it blowing on me when I'm boondocking in hot weather. Except when I flush the toilet. Thought I was gonna GAG. Now any midnight trip to the john is preceded by turning off the fan prior to flushing and leaving it off for about 10 minutes!

Having left you with that mental image, I'm going off list for now.

Paula

[Diesel1]

On my 67 I thought the vent was plugged because of the foul smells. It turned out to be a dirty tank, cause its an old trailer I guess. I put ice in the tank prior to a few road trips and presto.....no more horrible smells. Adios, John

[Arrowstream]

I had a black tank vent blocked solid by mud daubers. I would try pouring water down the pipe and if you get flow, flush it out with a garden hose. This method may also show if you have any poorly glued connections as water will shoot out of any bad joints.

[Gene]

You can also flush from the bottom. Using a Flush King, flush all the black water stuff out of the tank. This can take quite a few flushes. When it's clean (you could chlorinate it), just keep filling the tank until water comes out of the top of the soil stack (the plumbing name for the vent pipe). It will cascade down the side of the trailer and probably dislodge anything blocking the pipe. Don't have the fan door open while doing this.

How do I know this will work? Some campgrounds have much higher water pressure than others. In some, 4 minutes backflushing will not fill the tank. In others 2.5 minutes will bring a picturesque waterfall down the side of the trailer. It is pretty clean as the solids stay at the bottom of the tank. The toilet seal should hold as the water pressure should keep it closed. Because the water is under pressure, any leaks will be discovered very fast.

I know this will be found disgusting by some, and I have never done this intentionally, but if you get the black tank really clean, it could open up the pipe, or give you a good story. If it doesn't work, there's always beans.

Gene

[Ag&Au]

I am assuming that slow emptying of the tank is what is making you think it is blocked. I think it is more likely that a dam of TP etc is partially blocking the exit.

Do you have a way of observing the flow when emptying?

Fill the tank, and the watch the flow while emptying. Have someone open the flush valve in the toilet. If your vent is blocked, the flow should increase substantially.

If your vent is blocked, you should be able to hear the tank oil can (pop while flexing) while emptying, and if you have a clear section of pipe, you should be able to see a bubble go up the sewer pipe periodically, as that is the only source of air.

That's the end of my ideas.

regards,


Ken

[Aage]

Originally Posted by Foiled Again

My personal experience is that I know my vent pipe works. I had a second Fantastic Fan put in my bedroom... right next to the bathroom in the 25 FB. The mothership put in a bi-directional fan, and I LOVE to have it blowing on me when I'm boondocking in hot weather. Except when I flush the toilet. Thought I was gonna GAG. Now any midnight trip to the john is preceded by turning off the fan prior to flushing and leaving it off for about 10 minutes!

Having left you with that mental image, I'm going off list for now.

Paula

Ewwwwww! I just figured that out! When you flushed, that blew some of the aromatic exhaust out the stack.

Of course, your supre efficient fan then sucked it right into your trailer.

[Aage]

Originally Posted by Arrowstream

I had a black tank vent blocked solid by mud daubers. I would try pouring water down the pipe and if you get flow, flush it out with a garden hose. This method may also show if you have any poorly glued connections as water will shoot out of any bad joints.

I'm changing my mind on not wanting to do this. It does sound fairly safe, and there IS the added benefit of testing the pipe to make sure it doesn't have any leaks.

Originally Posted by CrawfordGene

You can also flush from the bottom. Using a Flush King, flush all the black water stuff out of the tank. This can take quite a few flushes. When it's clean (you could chlorinate it), just keep filling the tank until water comes out of the top of the soil stack (the plumbing name for the vent pipe). It will cascade down the side of the trailer and probably dislodge anything blocking the pipe. Don't have the fan door open while doing this.

How do I know this will work? Some campgrounds have much higher water pressure than others. In some, 4 minutes backflushing will not fill the tank. In others 2.5 minutes will bring a picturesque waterfall down the side of the trailer. It is pretty clean as the solids stay at the bottom of the tank. The toilet seal should hold as the water pressure should keep it closed. Because the water is under pressure, any leaks will be discovered very fast.

I know this will be found disgusting by some, and I have never done this intentionally, but if you get the black tank really clean, it could open up the pipe, or give you a good story. If it doesn't work, there's always beans.

Gene

Gene, I don't know which is worse, this method (golden showers) or the "Bean Blowout" system. I'm afraid neither will get used.

Originally Posted by w7ts

I am assuming that slow emptying of the tank is what is making you think it is blocked. I think it is more likely that a dam of TP etc is partially blocking the exit.

Do you have a way of observing the flow when emptying?

ken,

No, my only complaint is that there is frequently a "disharmonious" scent present. I had a drain problem which was caused by over-use of paper, but that problem has been solved some time ago.

Originally Posted by w7ts

If your vent is blocked, you should be able to hear the tank oil can (pop while flexing) while emptying, and if you have a clear section of pipe, you should be able to see a bubble go up the sewer pipe periodically, as that is the only source of air.

That's the end of my ideas.

regards,


Ken

Well that makes sense, and since I never hear the oilcan effect, I am now thinking that there are three possibilities:

1) I am imagining all this
b) There is a blockage, but not severe enough to create a vacuum strong enough to make the tank oilcan, or
iii) There is a blockage, but there are also air leaks in the pipe joints, enough to offset the oilcanning.

I'm going to try a water hose in the soil stack from the roof, and will report back as to my results!

Thanks to all of you.

[Becky B.]

Originally Posted by CrawfordGene

You can also flush from the bottom. Using a Flush King, flush all the black water stuff out of the tank. This can take quite a few flushes. When it's clean (you could chlorinate it), just keep filling the tank until water comes out of the top of the soil stack (the plumbing name for the vent pipe). It will cascade down the side of the trailer and probably dislodge anything blocking the pipe. Don't have the fan door open while doing this.

How do I know this will work? Some campgrounds have much higher water pressure than others. In some, 4 minutes backflushing will not fill the tank. In others 2.5 minutes will bring a picturesque waterfall down the side of the trailer. It is pretty clean as the solids stay at the bottom of the tank. The toilet seal should hold as the water pressure should keep it closed. Because the water is under pressure, any leaks will be discovered very fast.

I know this will be found disgusting by some, and I have never done this intentionally, but if you get the black tank really clean, it could open up the pipe, or give you a good story. If it doesn't work, there's always beans.

Gene

That's disgusting! Would it really come out the top? I'm just picturing the dump station at the campground with water spewing out the vent of my trailer. EWWWW!

[Aage]

Originally Posted by beckybillrae

That's disgusting! Would it really come out the top? I'm just picturing the dump station at the campground with water spewing out the vent of my trailer. EWWWW!

Trust me when I say that I'm NOT going to try to find out, Becky!

[2airishuman]

aage...

pooring water DOWN the vent tube is the simplest way to check for PLUGGING...

one SHOULD be able to smell some tank aroma AT the vent outlet normally.

if PARTIALLY plugged odors will still pass UP and water down.

IF totally plugged the water will either soften the plug OR evaporate.

unless the plugging is something ODD like sticks and stones and animal parts.

those things require other techniques to remove.
__________

using the flush king to force water UP AND OUT the vent tube is UNwise.

in g's case it was accidental,

and it is FORTUNATE something IN the tank didn't block this flow.

because it is VERY POSSIBLE to blow the toilet gasket or bowl seal OR break a retention bolt...

by pressurizing the tank with a flush king.

and those are the EASY things to fix.

one can also RUPTURE the connection of vent tube TO tank or drain values FROM tank...

these are much hard things to fix and all of these leaks are messy.

IF the vent tube is blocked AND the toilet bowl closed

air pressure OR water pressure from the FK may break things, don't intentionally try that.

everyting about the tank and drain and waste plumbing side is LOW PRESSURE sealed only...

cheers
2air'

[Aage]

Thanks fr confirming what I already had concluded, 2Air. This kid ain't gonna try no hi-pressure showers...

But I am still considering getting a Flush King.

[HiHoAgRV]

How about filling the black tank 1/2 way with fresh water...
add 1/2 a bottle of dishwashing soap...
then tow down the road sloshing the mess...
while a chase vehicle watches for bubbles coming from the roof vent...

[2airishuman]

Originally Posted by Aage

...But I am still considering getting a Flush King

yep, big fan of the f'king here...

search king and see what flushes up!

good to read u r home safely vernon...

YouTube - Tiny bubbles!

cheers
2air'

[Gene]

I like the half bottle of detergent approach if only because someone could make a video of the bubbling out the vent and post it.

Another approach could be to use a steamer (another of my suggestions I wouldn't try). And, Becky, yes, you can get a fountain out the vent and a waterfall down the side. I had flushed the tank pretty well before this happened, so it wasn't a situation where there was toilet paper and worse stuck to the trailer. The water was clear. It's best to laugh about it and hope no one saw it.

In post 13, Aage, you say "my only complaint is that there is frequently a 'disharmonious' scent present." One problem could be the deodorizer. They are not all the same and (unfortunately) we find the greenest ones last the least time, or sometimes we smell odor for a short time and then it goes away. One time it sometimes happens is when we stop after traveling for a while—obviously it shakes things up and they have to calm down. Then we don't have the odor until maybe the next day's travels. It usually means we will have to backflush the tank soon. Turning on the bathroom vent fan helps as a temporary solution.

You may not be getting the tank clean enough and that's why the occasional odor. There are a variety of ways to flush—the wand down the toilet, the integral Airstream system are two. I think the Flush King works well because you can see what's coming out. It is tedious because it can take quite a while and you can fill the vent. It's impossible to know just how full the tank is when you backflush and whether you have gotten everything off the walls. If there's stuff stuck to the walls and the water level is below that, some odor is inevitable. You can use the ice cube method to scour the tank, though we believe ice cubes go best with gin. Also we have found putting 5 gallons of water with the deodorizer after we have flushed the tank helps most in preventing odor. We find we have to flush the tank after around 6 to 8 days.

If the odor is only occasional, maybe there's no blockage. I don't know, but it would seem to me that a blockage would cause a constant odor.

And, finally, I was ready to squash that bug too.

Gene