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Old 10-29-2013, 11:47 AM   #1
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1972 21' Globetrotter
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Black tank overhaul: Thetford to Valterra tank fitting conversion/ plastic weld

I have gutted the rear bathroom due to floor rot from a poor shell to frame seal at the rear box and a leaking black tank among other things. So I have pulled the black tank. It has the white all plastic thetford valve fitting that I believe is glued in. I want to convert here to accept a Valterra valve. I have not been able to find any specifics on how to do this. Is there a simple glue/screw on conversion or do I need to remove the present one?

I also have cracks at the flange connection that I will attempt to plastic weld. I am a little concerned about what will happen here due to the possibility of not being able to seal correctly the glue used to mount the threaded flange connector in place. I believe this is LPPE material, but not sure.

I'm sure replacement may make the most sense due to above issues, but I will try to salvage if possible. Any input would be appreciated.
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Old 10-29-2013, 11:52 AM   #2
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Available at Amazon and most RV parts suppliers: Valterra T05-2285VP Thetford to Valterra Universal Adapter
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Old 10-29-2013, 12:08 PM   #3
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Thanks for the quick response awchief! I looked at the part you recommended. It seems to me that this is for a pre slinky conversion if i am not mistaken. I am looking for an immediately post-tank and pre valve conversion that will allow me to use a valterra valve, not just valterra hoses, etc. downstream.
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Old 01-22-2014, 01:39 PM   #4
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We're in a pickle trying to hook up our black tank with a Thetford mount to an appropriate collector (3x3 with 2x from the shower and sinks), onto ANY valve, Thetford or Valterra. Not only is the old Thetford valve cracked but so is the flange that attaches to the Thetford flange mounted in the black tank. Replacement Thetford valves can be had, and we actually have one in hand, but the problem is finding the fittings to attach black generic collector to the Thetford black tank fitting. Thetford collector seems to be unavailable. The pan is off the trailer; amazingly bathroom floor is A ok, although we did reinforce it some with added structural members. Awchief, I think the adapter you mentioned is for attaching a Valterra hose to the Thetford valve, the other end of the system from the black tank. I'm getting the idea that we have to refit the black tank with a Valterra flange and abandon Thetford entirely in our case. Any help from the experienced and wiser members would be greatly appreciated. Just hate to mess around the trying to make the black water tank secure with the new mounting. Is a new black water tank in our future? Sigh...
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Old 01-23-2014, 06:12 AM   #5
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Carolina-
I have gotten some great information on this forum, but was surprised at the lack of information on conversion to vaulters. Apparently valterra is not the only option, but in my opinion it seems to be the gold standard due to availability at RV stores, etc. And I have decided that probably the reason there is not more information is that my guess is that most people at this point just simply replace their older tanks instead of bothering to modify in any way.

Unfortunately for me, I take the attitude of if it's broke- fix it. If it can't be fixed- buy a replacement. So I took on two tasks with my above floor corner black tank: welding an almost complete crack around the spun weld flange fitting and a custom conversion of the Thetford tank gate valve fitting to a valterra one. All in all I have learned a lot and spent way too much time with this tank.

The welding: used harbor freight electric plastic welder ( about 80 bucks). It was hard to find the right material to weld(I believe ldpe). I started using cut up pieces from a bottle that would sort of blend. Then I switched to milk jug. Even worse. Finally I found a perfect match with a cutting board. There were no markings to be able to identify material, but it heated up just like the tank material and blended well. Basically when you heat the whitish plastic it will soften and turn glossy clear when it will blend with the donor which is heated the same. I had bought some welding sticks from HF also, but I couldn't find them at repair time. Not sure if they would work. It was tedious and took a long time. I think a small torch would probably do the job fine. I do have a before/ after photo that I will post later.

The conversion: so after waiting and hoping for a fix, I finally decided to make my own. My tank has a white thetford gate valve receiver. I am still not sure how it's connected. I tried to see if it was twisted on, but I was leery of pushing too hard and causing new cracks. So I grounded the notches off this fitting and sanded it to a smooth, flat hole. I took a 3" vaulters push on spigot fitting and cut the push on(pipe part) and kept the flat square piece with the gasket recieving ring on the opposite side. I sanded this smooth and flat. I glued the two smooth, sanded surfaces together with and glue (for the most part, black seems to be a reliable indicator of abs material, but I was assured that the white thetford was abs also). The glue seemed to make a good bond.

Afterthoughts: I have not leak tested it yet, having been busy with other projects. I am still considering self tapper screws in the abs glue joined area for extra reinforcement. The fact that the valve and hoses will hang off of this does not give the greatest confidence. I still have not retrofit the grey drain lines to fit. At some point I would like to add a grey tank inline to replace the final length of grey line. So I went ahead and purchased a grey valve that will just be left open on the sanitary tee. And finally, I really think it would be more time effective to just buy a new tank and get proper fittings if resources allow. Pictures are of thetford tank gate mount, tank mount modified to smooth ready for glue, modified valterra fitting now glued on which will receive gasket/ gate valve (I decided to glue it with bolts in place). Hope photos all attach.

And Carolina, I have my old connector and a few thetford hose fittings I won't be needing any longer. Once you go valterra...
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Old 01-23-2014, 01:23 PM   #6
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Thetford Valterra Conversion

Very creative job. Good work.
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Old 01-24-2014, 08:03 AM   #7
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1973 Argosy 24
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Wow--good work, Rippie.

Here is our played out setup:


Vintage Trailer Supply provided this work around:
"Thank you for your photos. After looking at them, It looks like the 08706 valve that you purchased will not work for what you need to do. You will need this valve instead:
08708 of Thetford valve 01447

Instead of an O-ring connection on the bottom (which is what you have with the 08706), the spigot connection on the bottom of the 08708 will be able to connect directly to the hub connection on the top of the Sanitary Tee, found here:
Sanitary Tee - Street Reducing 3" x 3"

Downstream of the sanitary tee, you will need the Thetford Bayonet, which will be solvent-welded to the bottom of the Sanitary Tee. Here is a link to the Thetford Bayonet:
Thetford Bayonet

To cap off your system, you can use either this Thetford Garden Hose Adapter:
Thetford Garden Hose Adapter

Or, you could use this Thetford Termination Cap:
http://www.vintagetrailersupply.com/Thetford_Cap_p/vts-337.htm"

We are considering adding a Drain Master hose system, so from the collector out, we'll use the Drain Master connector rather than the Thetford bayonet or Termination Cap. Posters here on Airforum seem to applaud the Drain Master hose. Any negative opinions out there?

We're working every day on our Argosy in hopes of being able to attend the Sebring Races in early March in her--phew!
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Old 01-24-2014, 09:46 AM   #8
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Carolina
I haven't tested my modifications yet, so I can't overwhelmingly recommend them. Although I am more confident in the valve adaptation than the welding. I went through your last post. Not sure where you are with purchasing these items. My biggest reason for choosing valterra over thetford was availability of parts and options for the future. I would still try to go with a valterra bayonet fitting to allow straight valterra fittings for hoses, etc. without having to add a thetford to valterra later. In other words, the farther upstream you can switch to valterra, the more money you will save and the easier it will be to find parts. And I also purchased a 1.5" valve for grey even though I still haven't quite configured the tank setup yet. If necessary, I will just attach to current plumbing and leave open until I can do it later.
I must also add this disclaimer: I am not speaking of quality of valterra over thetford. That would be the only reason I could think to nullify my recommendations. Maybe someone else can comment on that as I have no personal experience here.
I have found with almost every aspect of my resto there are many obstacles between ideas and execution. Good luck on your progress. When I started, spring was very far away.
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Old 01-27-2014, 12:00 PM   #9
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Carolinda, although the information we gave you is spot-on, I'm wondering if you have other choices. How is your Thetford valve flange attached to your tank? Could you post a pic? If you look at Rippie's tank, you'll see that it is a translucent white tank...like a milk jug. That is polyethylene. I believe yours is the same, but I don't know what fitting is between the Thetford flange and the tank. If we could figure that out first, we could give you the very best solution.
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Old 01-27-2014, 11:56 PM   #10
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I have a '74 Argosy 26' with a rear bath.
The BW tank outlet is a slip fit female fitting with a hose clamp.
There is a 3" PVC nipple attached to the BW dump valve which slips into the female outlet on the BW tank.
The BW tank dump valve outlet side goes directly into a 90* EL which connects thru a close nipple to another 90* EL. This forms an offset towards the left rear of the coach.
At this point it connects to a 3x2x3 sanitary T which is the connection point for the GW plumbing.
The sanitary T then exits the left side of the trunk where the Thetford adaptor is located.
If yours is like mine. I can send pics.
PM me if you would like pics.
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Old 01-28-2014, 08:17 AM   #11
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This first image shows the black tank with its welded Thetford fitting.
Thetford Set Up - Photo Gallery

My son and partner in our Argosy renovation has dug his heels in on re-doing the black tank weld, as our bathroom floor is surprising sound, and, while the pan is dropped, he doesn’t fancy working with hot plastic upside down. The black tank has no issues. By the way, our fresh water tank did have cracks around the inlet; son used milk carton material and welded the cracks slowly and in many layers. He learned from a couple YouTube videos—testing was successful and we trust this will be a sound fix for the water tank. He had that tank on the workbench—much easier than upside down. So, while your thinking, Rippie, is logical and preferable, I don’t think it’s in the cards, unless we here—rather you nice Airforums people--convince son otherwise.

Here is the old Thetford valve/connector setup:
Black Tank Fitting Argosy - Photo Gallery

We have very little room to add more stuff in this system—up to only ”, son estimates. Your system, Twinkie, sounds longer?

Steve, I very much appreciate that you are willing to revisit our valve issue. I’m both lazy and frugal and, hence, loathe re-doing work. Best to get it done right the first time ‘round.

Let me add a promo here—I had wondered just what “supporting members” meant, and found out that it means sending in $20 to Airforums annually. By reading here, I’ve saved scads of hours of work, buckets of frustration, and many dollars throughout our first project. $20 seems like a tiny price to pay to support this website. As you might imagine, in my opinion, we who benefit substantially from interaction with Airforums should become Supporting Members. Of course, responding to calls for advice, such as helping me out as you on this Black Tank thread have, contributes materially to Airforums, too, and it would be of less use without you. Thanks!
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Old 01-28-2014, 08:51 AM   #12
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Hmmm. Looks familiar. Your situation in General seems familiar as well. If you are willing to do a permanent conversion, I will explain how. The little regular white projections that form sort of a round dotted line- I used a grinder to sand those flush with the thicker ring above. This left a thick flat ringed surface for mating with the 3" Valterra slip on spigot square fitting surface (I similarly grinded the actual round hose part off of this, leaving only the square that you can see in my picture). These two abs plastic pieces were joined with abs glue. It is my understanding that this glue forms kind of a fusion, where two become one piece. Now you have the ring that will accept the valterra gasket where it should be. From there it is a piece of cake with the gate valve fitting on the other side and bolted in place with the four corner bolts/nuts.
From your photo it appears you have the necessary access to do it. I also understand that you have no room for mistakes, as the tank is in place. I'm not sure that I wouldn't also play it safe and use the correct fittings. You know they will work. Happy repairs! And, Carolinda, by the way, I think my phone was spell checking you into Carolina. Sorry, you have a pretty user name.
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Old 01-28-2014, 10:43 AM   #13
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Carolinda, I believe your solution is quite easy. You have a milky translucent polyethylene black tank with a female thread permanently part of the tank. You also have solid white ABS Thetford valve flange threaded into it. The Thetford flange has a male thread on its back side. You can unscrew the thetford flange. There are no adhesives holding it in. I know this to be true because *nothing* adheres to polyethylene. After you screw that out of there you will have a beautiful female threaded opening sitting there ready to screw this in: Valterra Male Thread Flange

Then mount your 3" Valterra valve and follow the rest of the instructions you received from us earlier.

Let me know if that doesn't make sense or if you run into any obstacles.
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Old 01-28-2014, 10:45 AM   #14
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Oh...also, it will be hard to turn that flange out. You may need to use a wrench or hammer. Polyethylene is strong stuff...stronger than the ABS after all these years...so be firm and expect the ABS to possibly break. The only reason not to be tough on it is if you have some reason to believe that you do not have a threaded connection...but I don't know how that would be possible.
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