Tank supports

[78Avion26F]

We have a 1978 26F. It has the same rear bath configuration as your 30P. Did you change out the 'flexible' black tank or stay with the original flexible one?

[silverloaf]

I don't know what you mean by "flexible tank". Can you explain?

The 3 tanks in our trailer have rigid walls. The bottom and top tend to float a bit and rely on supports from underneath to stabilize them.

[78Avion26F]

We have our black tank out right now. I just went out and looked at it. It was flexible on the 90 degree day when we pulled it and it was outside of the shed in the direct sunlight. It is a lot more rigid in the shade inside the shed on our 70 degree day. The top of the tank dips down 1 and 7/8 inches in the center. Guess it would hold a couple of gallons on top if it ever got wet? Makes me wonder about changing out the seal for the vent pipe.

[Rostam]

We have our black tank out right now. I just went out and looked at it. It was flexible on the 90 degree day when we pulled it and it was outside of the shed in the direct sunlight. It is a lot more rigid in the shade inside the shed on our 70 degree day. The top of the tank dips down 1 and 7/8 inches in the center. Guess it would hold a couple of gallons on top if it ever got wet? Makes me wonder about changing out the seal for the vent pipe.

78Avion26F,

Question for you: Can you take out the black tank without taking out the toilet?
Many thanks!

[78Avion26F]

You have to remove the toilet because it is bolted to a toilet flange that is screwed to the floor in four places. The toilet flange is made of ABS plastic which in turn is glued to a pipe at the top of the black tank. To remove the toilet flange from the pipe at the top of the tank cut out around the flange and make very shallow vertical cuts in the outside black ABS pipe that connects to the black tank. You should be able to break out the outer pieces of the toilet flange pipe without damaging the pipe on the black tank.

Black ABS toilet flanges can be found at Home Depot.

[Rostam]

Thanks a lot for the info! Very helpful.

[silverloaf]

Here are pics of the toilet flange I purchased for our trailer. Note that the tank end is threaded. Both the toilet flange and vent fitting are threaded into the tank.

At first observation, it appeared to be solvent welded. But a closer look revealed a female thread into the tank.

I'll install the flange after I install the finished floor.

BTW - There was a depression in the top of the blank tank. When I dropped the tank, I got a bath.
I'm not certain of the source of the water.

Also, ABS flanges are not available at our HDs. The alternative is to switch to PVC and use transition glue to tie them together.
https://www.homedepot.com/p/Weld-On-8-o ... 705041-_-N

[KYAvion]

Are the threads on a PVC flange different than the threads on an ABS flange?

[silverloaf]

I could not find a PCV threaded toilet flange at my local HD. I'm inclined to think they don't exist. The ones I found required solvent welding.

I did find a 3" PVC male thread adapter. It has the same thread pitch as my ABS combo flange. The adapter does not have a toilet flange. It would require a flange with a pipe size that would be inserted into the adapter.

I decided to do some tryouts between my ABS combo flange and the PVC adapter without the flange. In order for my ABS part to work, it would require compressing the tank so that the flange is tight against the floor. I measured 1/4" of deflection under full compression. I don't know whether compressing the top of the tank is a good idea.

When I installed the PCV adapter, the top of it is roughly 1-1/4 below the finished floor. I would have to find a flange with a 2" to 2-1/2" long tail piece to fit (maybe modify) into the adapter. This arrangement would not involve compressing the tank to make the flange flush to the floor.

I've attached some pics showing the parts I used for this study.