black water tank fixing - Fiberglass RV
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Old 03-03-2020, 11:24 AM   #1
Junior Member
Name: Bob
Trailer: Casita
Posts: 24
Angry black water tank fixing

We hit the black water tank to many times , and broke the drain off going in to the tank. Was on a trip so cobbled together a fix, however still a small dripping. I believe the tank it self is cracked as there is no way the pluming can leak.
My question is has any one opened the top of the tank? It looks like a simple job, but that can be deceiving . I would like to open the top to see the damage and if necessary to pour some fiberglass in order to seal it.

Advice? My Castia is a 95 model.
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Old 03-04-2020, 10:08 PM   #2
Senior Member
Name: Elliott
Trailer: Bigfoot
Posts: 395
Not too familiar with the Casitas specifically, so I can't visualize exactly what's broken very well.

Is it the hard black (ABS) plastic pipe that's broken? I think the "correct" fix is to cut it out and replace it, using ABS-specific adhesive. Second-best would be some sort of ABS patch.

If it's the tank itself, the first step is to find out what kind of plastic it's made of. A harder opaque plastic is ABS, and you'll patch the crack with a mix of ABS cement and ABS shavings. If it's a waxier more translucent tank that's polyethylene and you'll want to actually melt a polyethylene patch in (along with maybe some reinforcing mesh)

Either way, I wouldn't suggest trying to patch with fiberglass and resin. It might or might not seal well and stick to ABS, and it definitely won't bond well to polyethylene.
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Old 03-05-2020, 09:40 AM   #3
Senior Member
Name: Greg
Trailer: 2008 Casita 17 SD
Posts: 1,700
Not absolutely sure on such an older model Casita, but anything from the 2000's and on, you will find the black water waste tank is made from molded fiberglass, just like the trailer shell itself, and is pretty strong. Is your leak emanating from the "weep hole" under the trailer next to the drain line, or is it leaking from the drain piping itself?

On my Casita, the top of the waste tank is not only the tank cover, but is actually the mount for the toilet itself. With a little work, it can be removed for access, but it would be a last resort in my book. There's virtually nothing inside the tank that can't be reached by removal of the toilet itself.

If you still have any of the 3" black waste drain pipe still attached under the trailer, and you have a leak above the elbow, all is not lost. If you cut the black drain pipe close to the elbow on the horizontal portion, *cut it just short enough to be able to clear the frame when you unthread it off of the tank bottom fitting but leave enough to attach the flexible coupler, listed below. (Yes, the drain elbow has a female threaded upper connector and a glue-in lower, (horizontal,) connector for standard 3" ABS pipe. It's threaded into a threaded male fitting in the bottom of the tank.) After replacing the damaged components, you can re-join the ends of the black plastic pipe with a flexible coupling with screw clamp hose clamps.

Flexible connector:

This is just informational, but this is the threaded fitting that Casita attaches to the bottom of the waste tank. This is what the drain elbow threads onto.

If you need to replace the drain elbow, you'll want to get a 3" "Short Turn" elbow. Do not buy a "Street Elbow" because it will hang too low!

Here's a picture of what the black tank cover, with toilet mounted to it, looks like when new:
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Old 03-05-2020, 04:46 PM   #4
Junior Member
Name: Bob
Trailer: Casita
Posts: 24
thanks Greg, It looks like I just have to scrap away the seal , do something with the vent pipe, and it should pick up.
I will have to replace the spigot as the threaded part was broken up in the tank so will have to replace that and if tank is cracked then maybe some resin poured in the bottom will fix crack and attached spigot. At least that is what I am thinking, or planning.
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