Black tank vent pipe too long reducing capacity. DIY fix advice requested

[Cate&Rob]

TucsonJim
Cate&Rob

Did photo attach this time?

Erik

It did. You can choose a smaller size when you insert and folks can still click on it and enlarge to original. Once inserted, you can delete the attachment so it doesn't appear in both places. Minor issues . . . you got the picture attached .

Rob

[Popga]

It did. You can choose a smaller size when you insert and folks can still click on it and enlarge to original. Once inserted, you can delete the attachment so it doesn't appear in both places. Minor issues . . . you got the picture attached .

Rob

I ended up having to copy and paste... old fashioned but it worked!

Thanks,

Erik

[Kemper]

Hello everyone,

Kemper here posting an update on this project:

I got my borescope camera in the mail and was eager to take it for a spin. In preparation I flushed out the black tank best as I could. This included a normal tank dump followed by a high pressure spray down the toilet and filling the tank to the top using a garden hose. I had a flow meter on the garden hose and was a bit puzzled to find that the tank filled up at about 30 gallons instead of 37. I think the flow meter is specified to be accurate within 5%. Anyway, I dumped the tank again and got up on the roof.

I sent the tape measure down the vent pipe to the bottom so that I could see how far down the pipe I was as I fed the camera down the vent. As I got to the bottom I confirmed that the vent pipe was indeed 1.5 inches from the bottom of the tank.

Next, I sent the camera down the toilet and aimed it sideways toward the vent pipe. Not a pretty scene despite my best efforts to flush the tank out. I could see that the vent pipe was way deeper into the tank than it needed to be. It was about 3 or 4 inches plus the "barbed vent pipe coupler" at the bottom of the vent pipe which appears to be about 4 inches long. I have no idea what the purpose of the vent coupler is other than to decrease the effective holding capacity of the tank. If use of this part is standard practice, then the RV industry should reduce their published tank capacities accordingly, IMO.

Next, out of curiosity I sent the camera and tape measure down the gray tank vent pipe--even though I haven't had any gray tank capacity issues. This time I found that the bottom of the vent was 5 inches from the bottom of the tank. I had no good way to scope the gray vent pipe from the side so I moved on.

Next I scoped out the interior wall that contains the black tank vent pipe. I removed the thermostat (took out the screws behind face-plate) and the propane alarm (alarm lifts straight up from its holding bracket) to use the existing holes for scoping. I was able to check the pipe from floor to ceiling and confirmed that the pipe is not held in place by any hardware as others had mentioned.

Now I'm considering my next steps based on the helpful info and photos contributed in this thread:

1) Try to pull the vent pipe up until the coupler touches the top of the tank. I expect that the friction will be very high and I could damage the pipe. Also the top of the vent pipe is cut flush with the roof not giving me much pipe to grab onto. Then I would cut the top of the pipe flush with the roof again. Going this route will triple my current capacity but would still waste the top half of the tank because of the vent coupler.

2) I may have to go into the wall to be able to lift the pipe and execute option 1. Or I could cut a section out of the middle of the pipe and lift the lower section only and use a rubber coupler with hose clamps (mentioned above) to rejoin the two pipe sections. The interior wall would probably never look right after this operation--even after replacing the damaged trim pieces. Again, I'm still wasting half my tank capacity.

3) Similar to option 2, I could open the wall and cut the vent pipe in the middle AND at the bottom of the pipe near the floor. Then I could push the bottom of the vent pipe and coupler down into the tank where I would have to fish it out through the toilet hole (removing the toilet first). Then I could push the new bottom section of vent pipe down through the grommet extending into the tank by an inch or so. I would then use a rubber coupler to rejoin the top and bottom halves of the vent pipe. This would allow me to use almost all of the capacity of my black tank. Again, the interior wall may never be the same.

4) I could do 1 or 2 (or neither) and drill a bunch of holes in the pipe or coupler near the top of the black tank as mentioned above. Rotating the pipe to get holes all around may be a problem depending on friction.

5) Something else

Thank you all for your input and I welcome any additional comments.

[Cate&Rob]

Kemper

This is GREAT information . . . the detail that you have taken the time to provide will absolutely help others. What the heck is "the "barbed vent pipe coupler" at the bottom of the vent pipe which appears to be about 4 inches long." I have never encountered one of these. Please post a picture . . . we will "deal with" the surroundings . . .we have been there.

Be cautious trying to pull the pipe out through the grommet . . . the "failure mode" is where the grommet sticks to the pipe and pulls out of the thin wall tank top. (Ask me how I know this ) What might work (if you can gain access to the grommet) would be to grease the pipe, push it down through the grommet to lubricate the fit and then pull it up.

Rob

[howson]

Kemper

If option 1 is executed first, does that eliminate the possibility of doing the other options at a later date (if option 1's fix is not sufficient)? In other words (and if I read your post correctly) option 1 is the easiest and least intrusive repair. If the tank capacity gained is "good enough" -- no need to tear a wall apart. If option 1 doesn't provide enough extra tank capacity, then at least you've got the other two options still available at a later date.

The only other process I can think of is dropping the black tank as if it was being replaced. Not a fun job, but it will give you 100% access to the vent tube from underneath without damaging walls or messing with the vent on the roof. Unfortunately, though, the black tank is above the rear axle so it's going to be a hassle working in that area. The good news(?) is the slideout on your 22MLE is a Schwintek, so at least there's no thru-frame mechanism constricting access to the tank.

Howard

[Cate&Rob]

Kemper
The only other process I can think of is dropping the black tank as if it was being replaced.

I would exercise caution on this plan. Lifting a tank into place (particularly above the axles) while blindly inserting both the vent and toilet pipes into their grommets at the same time . . . sounds like a near impossibility.

Rob

[Jkwilson]

Kemper Thanks for posting the info. Those cameras are super useful when it comes to figuring out what is going on in areas you can’t see. You can look inside your brake drums, behind walls and inside plumbing. So helpful that you can start planning a fix instead of guessing.

[howson]

I would exercise caution on this plan. Lifting a tank into place (particularly above the axles) while blindly inserting both the vent and toilet pipes into their grommets at the same time . . . sounds like a near impossibility.

We've had a forum member replace their tank (twice!) due to user-error while black tank flushing. I can't find their thread -- sure would like more information on their experience. Hopefully they will see this thread and chime in on their experience. All I remember is him saying if it happens again he's done RV'ing!

[Kemper]

Kemper

What the heck is "the "barbed vent pipe coupler" at the bottom of the vent pipe which appears to be about 4 inches long." I have never encountered one of these. Please post a picture . . . we will "deal with" the surroundings . . .we have been there.

Rob

Sorry. I thought there was a photo above but I was confused. Here's a pic from the GDRV parts look-up page. The fat end attaches to the bottom of the vent pipe inside the black tank. The purpose of this part is a mystery to me. The thin end is (in my trailer) 1.5 inches above the bottom of the tank.

https://dpshop.granddesignrv.com/320032.jpg

[Cate&Rob]

Kemper

It looks to me like that part is designed to be all that pushes through the grommet. There is no way that end piece would be attached from inside the tank and pushing it through a grommet designed to fit to just the pipe diameter makes no sense.

Rob

[Jkwilson]

I agree with Rob here. Since the nomenclature for that part is “barbed vent coupler”, that would imply the smaller end grabs something to prevent inadvertent withdrawal, not that it’s fully in the tank.

My guess is that piece is supposed to snap into the tank grommet from the outside with very little of it in the tank.

Maybe whoever installed put the grommet on the pipe instead of on the fitting.

My hunch is the pipe is going to have to be cut, pulled out of the tank with the grommet, shortened to fit, then inserted properly and coupled to the vent pipe. No idea how much space you have to work with or how difficult that would be.

I think I’d send pictures and your other info to GD and see what they say. Looks like something they should step up and correct.

[Kemper]

Kemper here with an update:

RECAP:

I thought that I was having to dump my black tank much more frequently than should be necessary. Inspecting the inside of the tank showed that the vent pipe had been installed incorrectly. See my write-up earlier in this thread for the details.


OPENING THE WALL:

The vent pipe runs through the internal wall between the bathroom and kitchen. In the Imagine XLS 22MLE it’s a straight run through the floor and ceiling with no elbows to deal with.

First I had to remove some trim pieces. There’s a plastic end cap along the bathroom doorway that covers one edge of the panel I needed to get behind. Starting at the floor I cut the bead of adhesive that held the end cap onto the stud. I was careful not to crease or kink the end cap so that I could reuse it. I also had to unscrew some trim above the bathroom doorway to free the top of the end cap.

Next I pried the curved wall panel away from the bathroom doorway stud. The panel was secured using narrow (3/16” wide) staples. Staples also secured trim pieces along the floor and ceiling so I pried them loose as well.




FIXING THE VENT PIPE:

Now that the vent pipe was exposed I cut the vent pipe halfway between the floor and ceiling using a hacksaw. The top half of the vent pipe was fairly easy to move up and down. It seemed to be held in place by the friction of the roof membrane and insulation. I twisted and pulled up on the bottom half of the vent pipe until vent pipe coupler was snugged up against the gasket. (The coupler has a wide section that doesn’t fit through the gasket.) I confirmed that the pipe was pulled up as high as it could go by sending the snake-cam down the toilet and inspecting it from inside the black tank.

Next I cut the bottom vent pipe as low as I could against the floor stud with the intent of pushing the pipe/coupler down into the black tank and retrieving it through the toilet.

I cut a 10 foot piece of thin rope and stuffed half of it down the cut vent pipe into the black tank. I took a wire clothes hanger and formed it into a hook and used it to fish the end of the rope up through the toilet. Then I duct taped the rope inside the pipe to allow me to pull it up.



Next I started to push the pipe/coupler down through the gasket and into the black tank. The pipe went down only so far and then it wouldn’t budge. It was far enough down into the gasket where I couldn’t get a grip on it anymore. Hmmm. I sent the snake-cam down the toilet again and discovered that the coupler had bottomed out against the floor of the black tank. &%$#. Now I can't move it up OR down!

I headed to the local big box hardware store to look at tools and hopefully come up with a way to solve the problem. Eventually I decided to buy a Dremel set to get down into the pipe and cut it below the level of the gasket. The kit came with 1.5” cutting disks which barely fit inside the 1.5” vent pipe. Luckily, the vent pipe inner diameter is more than 1.5”

The Dremel tool was too fat for me to get the cutting disk deep enough into the pipe. Fortunately, the kit also came with a 3 foot extender cable attachment which allowed me to use the cutting disk remotely from the main tool. The hand grip of the extender is much thinner than the body of the Dremel tool and I was able to get the cutting disk further down the pipe.

Cutting with the Dremel was a very slow process. The disk kept stalling out and the motor unit was getting hot. The manual recommended a cutting speed of 10,000 RPM for plastics. Eventually I lost patience and tried 15,000 RPM and it seemed to cut much better. (I had also accidentally cut my rope in half so I had to retrieve the end from down in the black tank and tie it to the other half.)

Instead of taping the rope inside the pipe/coupler as originally planned, I decided to thread a square of cardboard onto the rope that was big enough not to pull through the pipe. This square would pull the pipe/coupler along as a pulled the rope up through the toilet. I wrapped the cardboard with duct tape for strength and waterproofing and taped a large flat washer around the cardboard square’s rope hole. Then I tied a large knot in the rope that wouldn’t pull through the flat washer and cardboard square. I carefully pulled the rope up through the toilet and guided the pipe/coupler up and out of the bowl.




That left a short piece of pipe scrap in the gasket to deal with. I glued a 1-1/4” diameter piece of PVC pipe into the scrap and waited overnight. I was able to pull and twist the scrap piece out of the gasket the next morning.

Originally I was planning on just pushing the vent pipe down through the gasket and into the black tank a couple of inches. However, the pipe and coupler assembly was long enough that I could reuse it. I reconnected it to the bottom half of the original vent pipe using a Fernco coupler and pushed it down into the gasket.

I pushed the upper half of the vent pipe up through the roof a bit and used a 2^nd Fernco coupler to rejoin the upper and lower halves of the vent pipe. Vent pipe problem solved!




CLOSING THE WALL (a work in progress):

Now I need to close the wall back up. I’ve been searching for a 3/16” wide stapler similar to the one that Grand Design used to install the wall panel. Most staplers are significantly wider which makes for a more unsightly repair job. I may have no other choice. If I recess the staples and fill the divots with colored compound, the repair may not be too obvious.

I’ve considered using pin or brad nails as well. These nails have no head and the wall panel and trim material are too thin for a headless nail to hold them in, I think. There isn’t enough friction there to prevent the nail from pulling through. A staple, however, surrounds a bigger piece of material to attach it to the stud making it more secure.

I’m also planning on securing the electrical wiring so that it can’t rub on the Fernco hose clamps or get pinched when I close the wall. I’ll follow up with details on how I finish it.


IN CONCLUSION:

I’ve left out various dead-ends and trips down rabbit holes for the sake of brevity (believe it or not). Hopefully this posting will help others in my situation have an easier time of it.

Once again, thanks to everyone for your advice, technical information and comments. I couldn’t have completed this job without your help.

[Jlawles2]

Kemper, What you are looking for is a narrow crown stapler. Usually they are 1/4" wide 18 gauge. Pasload does make a smaller one but your local orange box store will have the std 1/4" ones pretty much in stock.

If you are not too worried about too life you can try https://www.amazon.com/Grex-2116AD-S.../dp/B008B76YHM

Several other companies also make fine gauge ones, but they get pricey when you start looking at the production Senco stuff (22 gauge https://www.senco.com/senco-tool/sft...-auto-stapler/)

[Jkwilson]

Thanks for the follow up. Posts like this help a lot of people. It’s always a journey of discovery doing a job like this.

Let us know how it works.

[TedS]

Kemper regarding pin nails, drive them at an angle instead of straight in to give the headless pin a better grip.