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Old 11-27-2011, 08:39 AM   #1
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1986 34' Limited
1966 24' Tradewind
Conifer , Colorado
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Holding Tanks Drain - Thetford to Valterra Rebuild

Greetings Airstrem Enthusists,

You folks on this sight have been very helpful to me in past projects. Now on to the next big thing.

It's time to replace the slide valves on my 86 Classic. I want to change to modern Valterra slide valves and the 3" Valterra discharge port. My Airstream is factory built with the old Thetford "3 1/4 iinch" piping and connectors that we all have trouble connecting to.

Can anyone point me to a "how to" thread or instruction as a guide for this project for this year Airstream? I have searched Airstream Forum and did not find the exact information I wanted. My trailer is newer than some of the projects I read about. I figure I am going to have to cut off the Thedford slide valves, and "fiberglass" connect the right size piping to the tanks to fit up a Valterra slide valve. I figure once I get to the Valterra slide valves and 3" piping, I can plumb my "Tee" connector and discharge port in the standard 3" stuff. And I will fabricate a decent access panel in my tank cover making servicing the valves easier.

I like my Thedford 12v macerator pump as my Airstream discharge port is low, and the campground sewer connectors are usually higher once I get the elbow and slinky set. We all know sewer water won't flow uphill. I had difficulty converting my macerator 3" bayonet connector to the goofy Thetford 3 1/4 discharge port. I finally did so and now I can pump the sewer water uphill to the sewer drain easily. In fact, I can squirt it high into the air if I wanted to! Funny how campers next to my site seem to pull out after one night. At least I don't have to do the famous Airstream slinky lift anymore to get the thing to drain!

So on to replacing the slide valves and discharge port. Any help or experience in this project will be greatly appreciated.


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Old 05-27-2012, 04:37 PM   #2
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1986 34' Limited
1966 24' Tradewind
Conifer , Colorado
Join Date: Jun 2009
Posts: 2,520
Thetford to Valtera Project Done

I just finished rebuilding the dump valve manifold on my Airstream. The old Thetford valves were leaking a little. And I hated the old 3 1/4 bayonet connector on the discharge port. Here is what I learned.

Valtera pieces and parts are readily available. The valve is well designed. It has just two seals compared to the old Thetford 3 round seals and a gasket. I like the way the Valtera valve bolts together. The Thetford uses self cutting sheet metal screws.

The belly tank pan is actually the support for the tanks. Dumb! There was 1" of old styrofoam insulation around the tanks. Getting this big 5' by 4' galvanized pan off was a bear. Lots of rusty bolts. The tanks gotta be empty!

The tanks appear to be a polyelthyene. The drain pipe connects to the tanks with a hose clamp! My tanks had calking around the connections. The black tank is held up by the toliet flange and the vent pipe on the curb side of the tank. The gray tank is held up by the drain pipe itself and the curb side vent pipe. The tank pan is the actual support for the tanks. These tanks weigh over 250 lbs full, why they aren't more secure I don't know.

I used 3" PVC pieces from the hardware store to plumb the drains. I made it like the old one. It was a challenge to get all the pieces to align during the gluing phase. The only thing holding up the drain maniford is the two hose clamps at the tank connections and the tank belly pan.

All the jostling of the tanks while fitting the drain manifold popped off the gray drain line connection under the shower, and the black vent pipe connection under the rear furnace. Luckily I was able to get both reconnected.

You can't fill the tanks to check for leaks until you get the tank pan back under the tanks for support. Then you can't see any leaks. I mounted the tank with new bolts, and then filled both tanks with water and hoped for the best. Lucky me, no leaks yet. But I won't know for sure until I bounce them down the highway.

So it's done. Cost in parts was about $200. If a Valtera valve starts leaking or gets jammed, the only way to service it is to drop that darn tank pan.


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Old 05-27-2012, 05:22 PM   #3
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I think most of us with old trailers have a panel cut out of the tank pan with a piece of sheet metal screwed on it. You can access the plumbing. Probably would have to take the pan down if a tank itself is leaking.
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Old 05-27-2012, 06:41 PM   #4
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I got a new black tank for my 68 from Andy. It had a flange around it so I drilled and screwed it to the floor from bellow this is what is supporting it now. There why just scared me. Plus I can get to everything without dropping the tank.

May you have at least one sunny day, and a soft chair to sit in..

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Old 05-27-2012, 06:49 PM   #5
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Originally Posted by Bill M. View Post
I think most of us with old trailers have a panel cut out of the tank pan with a piece of sheet metal screwed on it. You can access the plumbing. Probably would have to take the pan down if a tank itself is leaking.
Bill, mine has that screwed on panel. I had not really thought about it but went out and pulled the screws out after reading you post. Sure enough the plumbing was exposed under it. Thank you for bringing this up.
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Old 06-08-2012, 03:34 AM   #6
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1986 34' Limited
1966 24' Tradewind
Conifer , Colorado
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Pictures of Thetford to Valtera Drain Plumbing Rebuild

Here are some photos I took during my project. I thought they may be helpful to someone doing a similar project on a similar Airstream.

Photo 1 The gray tank Thetford was leaking a bit. And I didn't like the Thetford 3 1/4 bayonet connector.

Photo 2 The tank support pan is big and awkward. I used my floor jack and a 2x12 to support it and wheel it out. I was surprised to find cheap styrofoam liner in this pan. I replaced the styrofoam with a good quality 1" foam insulation. The tank support pan holds the tanks up.

Photo 3 The tanks appear to be polyethylene. The 3" inside diameter drain holes are as molded. The whole drain valves and piping are mounted with hose clamps! The gray tank is hanging by the shower drain connection, and the vent pipe connection. These are also hose clamps. The tank support pan does add support to the drain plumbing once in place.

Photo 4 I plumbed the new Valtera valves in place with PVC pieces from the hardware store. It is tricky to get the exact locations for the tank drain hole positions.

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