Home Made black water tank

[Wavery]

I am in NO WAY suggesting that this is a reasonable solution for a black water tank. It's more work than most people want to do..... even experienced fiberglassers. There isn't much area to work in there, the temperature is hard to control and the fumes are horrendous.

My original plan was to make a male mold, fiberglass it then move the finished tank into the TM. That would lose me about 1G of storage. My goal was 13G and the only way that I could get that without making the tank uncomfortably high for my 5' tall wife was to build the tank in place. Again, I don't recommend it.

This tank is 4 layers of F/G (1st coat mat, 2nd coat woven roving, 3rd coat mat, 4th coat biaxial cloth) 2 coats gelcoat on 1/4" thick plywood frame. It holds 14G but 13.5 is reasonably full.

[rich2468]

Pretty cool. Thanks for sharing your handiwork!

I see you have both a clean-out and a vent. Will both of those be routed under the tub to the underside of your TM?

[Wavery]

Originally Posted by rich2468

Pretty cool. Thanks for sharing your handiwork!

I see you have both a clean-out and a vent. Will both of those be routed under the tub to the underside of your TM?

The vent will go straight up and through the wall to the outside. The clean-out will go across the back of the toilet, through the sink cabinet and down through the floor. It came with a bracket that hangs on the frame.

[Bill]

What a piece of work! I'm glad you recommended that I not try it. I was about to see if I could knock one out before dinner!

Seriously, I'm very impressed. Keep us up to speed with any news.

Bill

[Wavery]

It would be so easy and cost effective for TM to have a custom, drop-in, black water tank made. Once the mold is made, the rest of the process is easy. They could even have blow-mold tanks made. They are relatively cheap and easy. There are a lot of companies that will build them (in bulk) from dimensions over the internet.

On my next TM, I will build a "female mold" for a tank. That way I can lay up the F/G in my garage and have a lot more control over the lay-up process. The entire F/G process could be done in 1-day, with no sanding, leveling, breathing all those fumes and dealing with a big mess inside the trailer. One big problem with this project was not being able to move around the project.

I've done hundreds of F/G projects and this was one of the hardest ones that I've done.

[jagizzi]

Nicely done! Did you use Epoxy as the resin? I've never known the fumes to be strong so am wondering if you did something different from what I am used to.

[Bill]

Originally Posted by Wavery

It would be so easy and cost effective for TM to have a custom, drop-in, black water tank made. Once the mold is made, the rest of the process is easy. They could even have blow-mold tanks made. They are relatively cheap and easy. There are a lot of companies that will build them (in bulk) from dimensions over the internet.

You are right - TM could easily make and install a black tank, but that is not the issue. The difficulty that TM faces is that plumbing code, including RVIA code for campers, requires the black tank to be vented through the roof. Venting through the sidewall or floor is expressly forbidden, as is any design that requires action (such as connecting a pipe) by the owner/user. In a folding trailer, this is a nearly impossible requirement. TM has struggled with this since Thetford discontinued the recirc, and has not yet (in my opinion) found a good solution.

Bill

[Wavery]

Originally Posted by Bill

You are right - TM could easily make and install a black tank, but that is not the issue. The difficulty that TM faces is that plumbing code, including RVIA code for campers, requires the black tank to be vented through the roof. Venting through the sidewall or floor is expressly forbidden, as is any design that requires action (such as connecting a pipe) by the owner/user. In a folding trailer, this is a nearly impossible requirement. TM has struggled with this since Thetford discontinued the recirc, and has not yet (in my opinion) found a good solution.

Bill

They figured out a way to do it when they started installing the Sealand toilets.
However, it wasn't very attractive nor was it very creative. I think that it could be done with PVC pipe.

[Shane826]

Looks good! Did you slope the bottom towards the drain? That’s one of the biggest fails of the Dometic SeaLand, the bottom of the tank is just flat. Also I’d recommend putting a gate valve directly under the floor on the drain pipe. Otherwise everything wants to collect in the downpipe leading to the dump valve.

[Wavery]

Originally Posted by Shane826

Looks good! Did you slope the bottom towards the drain? That’s one of the biggest fails of the Dometic SeaLand, the bottom of the tank is just flat. Also I’d recommend putting a gate valve directly under the floor on the drain pipe. Otherwise everything wants to collect in the downpipe leading to the dump valve.

I put in several layers of mat, tapering the layers toward the center of the tank. Hard to tell in the pic because my last layer was a single piece of 2ozbiaxial cloth. I'm not proud of the finish look of the inside of the tank
(because of the difficulty involved) but no one will see that once the top is sealed on. The washout jet should help as well. I'm not too concerned about what settles in the elbow.

What I am concerned about is the ABS pipe getting hit by something and fracturing the mechanical bond between the F/G and the ABS pipe. I did a test piece before I did it this way and it was impossible to break the bond. At some point, I will cut the ABS pipe under the trailer and put in a clamp on, rubber connector. That way, if worse case scenario happens, the pipe should separate at that connection before it causes any damage to the tank.