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SilverHoot 10-26-2009 04:10 PM

A simple question.
I'm in the process of putting a new but not OEM black tank. The interior is gutted and the rear portion of the floor removed. I'm working on mounting the tank and am wondering how close to the bottom of the sub floor it needs to be for the toilet flange. Is the toilet flange height somewhat flexible as far as what height it can be made. The tank does not have a threaded fitting installed yet. The top original tank was mounted right up against the sub floor. I think I'd like to have about an inch or so of space for some insulation. Hopefully a long winded question for an short and easy answer. Oh thought of another question, what type of toilet flange? Thanks.

SteSpot 10-26-2009 06:39 PM

No such thing
I clicked on this thread to see what a simple question is like and I am sorry that I cannot help you. It doesn't seem like a simple question to me. But I am sure there are others that have the answer to your question and it may be simple to them....anyway....good luck on your project....I hope you have your answer soon. pj

68 TWind 10-26-2009 07:20 PM

Silverhoot, your question is why I went with an OEM type replacement in my 68 TW. Just too many other things to spend my time on. Good luck and let up know how what you decide to do.

SilverHoot 10-27-2009 06:55 AM

68Tradewind, I would have probably gone OEM type too if $$$ were no object and I was not also adding a grey tank that I hope to wye into the black dump valve. I will be gaining a few gallons of additional capacity for my troubles.

easyride 10-27-2009 07:01 AM

Buy your female,and your flange,measure how much room they take up,don`t forget the thickness of your floor.You should then be able to determine clearance required.Dave

SilverHoot 10-27-2009 07:40 AM

Thanks Dave, I think I can figure out how much the female and the flange will take up. Say the distance that they take up is 1.5" and I need it to be 3", how do I gain the additional 1.5"? Probably as simple as a 1.5" piece of 3" ABS, but have never done this before so am unfamiliar with the setup.

easyride 10-27-2009 07:51 AM

Your flange screws into the female,it would be very hard to add 1.5 " to that,why do you want the insulation?? Dave

Minno 10-27-2009 08:31 AM

I think all black tanks mount directly to the bottom of the plywood floor. Either by a flange that screws directly to the plywood, or held in place by straps or a metal box like on my 72 Sovereign. The female threaded fitting that goes into the tank gives you maybe an inch of play room when you screw the toilet flange in, so you can put a wood floor on top of the plywood subfloor, but that's about it. I'm also wondering why you want insulation on top of the black tank? If you're going to heat the tank for winter camping, having it mounted directly to the subfloor will help with keeping the tank above freezing.


SilverHoot 10-27-2009 08:39 AM

I'm going with rigid insulation and would have just attached it to the bottom of the plywood with a small air gap. Another reason I was thinking of mounting the black tank a bit lower, is I thought it would help with the dump plumbing slope of the grey tank to black valve. Sounds as though the black tank can't be much below the floor though.

Minno 10-27-2009 09:01 AM

I was thinking about this a bit more, and I wonder if you could use a regular house toilet flange instead of the threaded one normally used in RV's? You’d have to make sure you can mount the toilet to it and get a good seal of course. But, since you do not have a fitting on your black tank yet, then instead of using the normal RV style threaded fittings, you could use house style glue fittings. Use a glue type 3” fitting on top of the tank, run a short length of 3” pipe up and glue the toilet flange on. The toilet flange would still screw to the floor, so it would be a solid connection. I don’t see why this wouldn’t work, but I’ve never tried to put an RV toilet onto a house style toilet flange. They certainly look to be the same, but I never measured them.

The only downside I see of gluing everything together is future maintenance or leak issues. Instead of unscrewing the threaded fittings, you’d have to cut the pipe to drop the black tank.

Anyone have any thoughts on this?


SilverHoot 10-27-2009 09:29 AM

What about this?
1 Attachment(s)
Was wondering about something like one of these might work?

SilverHoot 10-27-2009 02:29 PM

Got it!
Got it I think. Went to an RV parts store and is pretty simple My tank will have a female 3" threaded, then a 3" x 3" threaded nipple, then a female 3" toilet/floor/closet flange.

Minno 10-27-2009 02:47 PM

Cool! :clap:

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