First a cracked gray tank, now a cracked black tank...

[JDBrown]

Originally Posted by InterBlog

I'm late to this party, but the OP is talking about the tank itself cracking? Not the joinery?

Different model I know, but first generation Airstream Interstates are notorious for piping splits. They were plumbed without any way of allowing for flexure during rough rides. The very first big DIY job that my husband and I did was to re-plumb most of our system because most of the connections had been sheared apart.

If the OP replaces one or more tanks, I would recommend a similar provision be evaluated, and also maybe add a relief valve to any tank that could disgorge an overflow into the van itself, if that is a possibility in his/her model.

It might not have been plumbed that way to start with, but if you are in for a penny, you might as well go in for a pound, so that it could never morph into a new problem down the road.

You can read about our plumbing retrofits here.

Thank you for the advice, I'll definitely check out that link. When I got the tank off, I discovered that it wasn't cracked, it was melted by heat from the exhaust (next to the muffler). So I'm now trying to determine if my exhaust is obstructed.

[vwmaniaman]

You may have a worn out O2 sensor causing your convertor to work harder and get too hot. On our older vans 60K is used up time.

[JDBrown]

Originally Posted by vwmaniaman

You may have a worn out O2 sensor causing your convertor to work harder and get too hot. On our older vans 60K is used up time.

That's good to know. I've done a vacuum pressure check which seems to indicate that the exhaust is not obstructed, and the guy at the local muffler shop seems confident that the kind of heat I'm seeing is due to the engine running rich (I think someone already suggested that earlier in the thread).

So I have an appointment with the mechanic on Tuesday. Unfortunately this is looking beyond my ability to diagnose on my own, and I REALLY don't want to risk melting the tank again.

I've also been working on patching the black tank so it's ready to go back on once the heat issue is resolved. I'll post photos if I ever figure out how.

[hbn7hj]

Originally Posted by JDBrown

I've also been working on patching the black tank so it's ready to go back on once the heat issue is resolved. I'll post photos if I ever figure out how.

You seem able to solve the problems. Reduce the heat output and put in heat shields. Hopefully you have the space to put in the thin steel plates with an air gap. Don’t know if yours had them but that is what Roadtrek used in the later models.

Is there a metal plate (heat shield) to protect the floor? Later versions had that.

The original heat protection worked all those years. It can be made to work again.

[JDBrown]

Originally Posted by hbn7hj

You seem able to solve the problems. Reduce the heat output and put in heat shields. Hopefully you have the space to put in the thin steel plates with an air gap. Don’t know if yours had them but that is what Roadtrek used in the later models.

Is there a metal plate (heat shield) to protect the floor? Later versions had that.

The original heat protection worked all those years. It can be made to work again.

Yes, it has the thin steel plate heat shields between the exhaust and the tanks, and also between the exhaust and the floor. It seems pretty clear at this point that the exhaust got far hotter than it ever should on last weekend's trip. Now it's just a matter of figuring out why and correcting it.

[Average_alice]

I'm seeing that you are working on restoring your black tank but have you considered installing a porta-potti in it's place? No more dump station trips. That's what we did on our 200 Versatile with a Thetford 335, 2.5 gallons (not too heavy to carry). But we also use a bucket composting toilet as part of our overall "system". We mainly enjoy boondocking.

[InterBlog]

Originally Posted by Average_alice

I'm seeing that you are working on restoring your black tank but have you considered installing a porta-potti in it's place? No more dump station trips. That's what we did on our 200 Versatile with a Thetford 335, 2.5 gallons (not too heavy to carry). But we also use a bucket composting toilet as part of our overall "system". We mainly enjoy boondocking.

Where do you dump the Thetford 335, if not at a dump station?

[Average_alice]

They can be dumped in any public toilet. But we're generally not doing that - I don't know how much detail you want to hear on this sensitive topic - We're practicing "separating the liquids from the solids" as they do with the commercial composting toilets like the Nature's head, and we only use the porta potti for liquids, which is perfectly fine to spread around on the plants at our remote boondocking sites. We use our composting bucket with kitchen trash bag liners for the rest (except TP). It saves on water too and our grey water is now clean enough to sprinkle around as well. I mean it's not just a luggable loo, which is too small - we made a custom toilet seat - now perhaps I'm going into too much detail... Of course if we're at a campground we might use the bathrooms there to save work, except now there's the coronavirus worries, so maybe not?

[Gritty Eileen]

I had a dumping dilemma with an older rig [25yr]. The gate valve stuck. Replaced the valves - plastic very brittle. Just bought a roadtrek 1996 chevy 210 popular and had the waste tank assembly replaced. I'm planning on replacing the toilet since valve is sticking. The RV had not been well cared for.

[JDBrown]

So here's an update for you all. I've spent a fair amount of time under the RT this past week, and it looks like there are a LOT of missing or broken-off screws that should be securing the sheet metal heat shield between the muffler and the waste tanks. Without those screws in place, the heat shield can swing back and forth enough to touch the black tank, which is what happened. I also found some plastic melted onto the heat shield, so I know it actually touched and it wasn't just radiant heat that melted the tank. And knowing that's it's completely normal for the exhaust system to get upwards of 600 degrees F, and that ABS plastic melts around 200 degrees F means it's not at all surprising that hot metal touching the tank will melt it. Makes me feel better, as I'm now more confident that I can just put in new screws wherever there are holes, properly secure the heat shield, and get back on the road.

I'm still taking the van to the mechanic tomorrow, just in case and for peace of mind. And I think I might still fabricate another sheet metal heat shield to go around the muffler. But I'm a lot less freaked out about the prospect of this happening again.

As for the suggestion to replace the toilet with a composting porta-potty, that's a no-go for me. That was one of my wife's conditions when we started looking at RVs--it has to have a toilet we can flush and then empty the tank at a dump station. No pulling out an insert from under the throne and lugging it to a public toilet or other location, just hook up the dump hose and pull the valve. So, in the interest of marital harmony, I'm not even considering switching to a composting model. Plus there's the fact that we're a family of 5 (yes, 5 of us in a Class B--2 parents, 2 teenagers, and an 8-year-old). The 13 gallon black tank isn't what you'd call big, but it's a fair sight bigger a 2.5 gallons.

Hopefully I'll have more concrete information after I get back from the mechanic tomorrow. In the meantime, here are some photos of the melted tank, and of my (still in-progress) repair job.

[rowiebowie]

You're a handy guy. Looks like your're getting the pieces back together. And I mean pieces.

[GroupB]

What's your method of adhesion for the tank repair?

[JDBrown]

Originally Posted by GroupB

What's your method of adhesion for the tank repair?

In short, LOTS of ABS cement.

Here's the more detailed version:

1. I started by taking a section of ABS pipe and cutting a slit down the length with my table saw. Turns out that might not have been such a good idea, as I then had to scrape plastic off the blade with a putty knife (I keep forgetting about the low melting point of ABS, even though that's largely what got me into this predicament in the first place).

2. I used a heat gun ($15 at Harbor Freight) to heat up the slit pipe until it was flexible, and then pulled the slit apart to flatten it out. It took several heating/bending cycles to get it basically flat.

3. I CAREFULLY used the heat gun on the tank to flatten out the worst of the melted areas as best I could, pushing the soft plastic back into shape with my fingers (wearing leather gloves). This was the most nerve-wracking step, as I really didn't want to make the damage any worse.

4. I cut a section of the flattened pipe to the desired size, and then heated it back up with the heat gun. Then, while it was still flexible, I pressed it into the contours of the tank at the location where I wanted to place it. When it cooled, my custom patch fit the spot perfectly, with very little gap anywhere.

5. I roughed up the area around the holes (anywhere I thought I might need ABS cement to stick) with 150 grit sandpaper, and then I wiped the whole thing down with acetone to remove any oils that might inhibit adhesion.

6. I slathered on a bunch of medium black ABS cement around the hole and on the back side of the patch, and then pressed the patch into place, holding it there with 1 or 2 large squeeze clamps.

7. Once the cement was dry, I laid down a thick layer of more ABS cement overlapping the joint of the patch and the tank, pressed a bit of fiberglass window screen into the wet cement, and covered it over with yet more ABS cement. (I'm still working on this part, as I ran out of ABS cement, and haven't made it back to the store).

8. After that layer of ABS cement dries, I'll add one more coat, give it 24-48 hours to dry, and then leak test it. With any luck, I'll be good to reinstall the tank at that point. :Fingers Crossed:

This is a much more extreme version of what I did to fix the small crack/cut on my gray tank; that was just ABS cement, fiberglass window screen then 2 or 3 more coats of ABS cement.

[hbn7hj]

Originally Posted by JDBrown

I'm still taking the van to the mechanic tomorrow, just in case and for peace of mind. And I think I might still fabricate another sheet metal heat shield to go around the muffler. But I'm a lot less freaked out about the prospect of this happening again.

Don’t forget about the DEI titanium heat shield fabric. I used it to cover the top of the catalytic converters with air gap to lower the inside floor temperatures behind the front seats. The temperatures were very high but I didn’t get a number.

[InterBlog]

Originally Posted by Average_alice

They can be dumped in any public toilet. But we're generally not doing that - I don't know how much detail you want to hear on this sensitive topic - ....

My concern is not a TMI concern. My concern is that some "alternate" toilet suggestions are not intellectually honest. I am not accusing you of being that way - but I've seen it time and time again on multiple forums: ideology eclipsing logistics. Where are people who are using these toilets dumping their urine?! I still don't know because almost none of them will 'fess up. Is it being discharged directly to the environment in an uncontrolled manner? In many scenarios, I think it must be, because I cannot detect any other alternative.

It's one thing to be surrounded by tens of thousands of acres of woods where urine could be distributed naturally and would not impact the environment. But I'm afraid that a lot of the vanners are simply dumping it in ditches in more populated areas. Total nitrogen (TN) in urine is around 9,000 mg/L - it is not without its own pollution issues. It is not the pure, innocent non-waste substance that many "alternate" toilet proponents declare it to be.

[InterBlog]

Originally Posted by Gritty Eileen

I had a dumping dilemma with an older rig [25yr]. The gate valve stuck. Replaced the valves - plastic very brittle. .....

I recommend that everyone carry replacement gate valves in their onboard emergency kits. Those things are cheaply made and they fail like clockwork, often without warning.

Here's a picture of my husband on the ground in Nova Scotia. He was scheduled to fly up to meet me (I drove), and in the 2 weeks between the time that I left Houston and his arrival, our relatively-young (3 years) black tank gate valve failed.

He walked off the aircraft, whipped a gate valve out of his carry-on bag, and hit the ground to replace it because we were living in the van exclusively and so that job couldn't even wait until morning (I was in a local area where I could not buy a replacement myself - there were none available).

[booster]

Where is the big puddle of "mess" and the nose plug that is normally seen in this repair?

[GeorgeRa]

I never had to fix the dumping gate valve on my cassette, it never got brittle, it never got stuck closed, it never got stuck open, it never leaked, it never generated a puddle while being fix, I can say - a perfect valve.

[Bud]

Originally Posted by GeorgeRa

I never had to fix the dumping gate valve on my cassette, it never got brittle, it never got stuck closed, it never got stuck open, it never leaked, it never generated a puddle while being fix, I can say - a perfect valve.

Darn, thanks George. I just had not thought about it, realized it. Also have 2 of those "perfect valve"(s) associated with my grey and back tanks, 13 years now. Lubrication makes a difference. And there noticeably less use vs a small cassette thing.

Bud

[GeorgeRa]

Originally Posted by Bud

Darn, thanks George. I just had not thought about it, realized it. Also have 2 of those "perfect valve"(s) associated with my grey and back tanks, 13 years now. Lubrication makes a difference. And there noticeably less use vs a small cassette thing.

Bud

My experience with black tanks was OK, just didn't like dumping and cleaning afterwords. I agree, lubrication was important, I often use "Drain Valve Lubricant" and occasionally vaseline directly on the valve. But, no valve no maintenance .