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Old 07-11-2010, 01:26 PM   #1
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1966 22' Safari
Davis City , Iowa
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Question How do you attach the fitting to the black tank?

I bought a new black tank last year without the fittings attached since I didn't know exactly where they should be placed. I changed the size of the black tank and also bought a new toilet so the new hole is in a different spot than the old one. I planed on cutting a hole and using ABS cement to attach it and I also bought a 3 1/8 hole saw from BAHCO. This was based on the recommended size listed in one of my RV catalogs. Now that I'm ready to cut the hole for the fitting, (to hold the flange) I realize the hole saw's diameter is less than the diameter of the fitting. Did I buy the wrong size or is there some trick to attaching this? If someone could let me know how to accomplish this task I might have this thing on the road in three weeks. (fingers crossed) Thanks
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Old 07-11-2010, 03:21 PM   #2
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2002 25' Safari
1977 20' Argosy 20
northern valley , new jersey
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pipe size

"nominal pipe size" is not the actual "outer diameter" or "OD" of a pipe, it's generally close to, though not necessarily exactly the sames as the "inner diameter" or "ID" of the pipe.

thus the actual OD of a piece of pipe can be very different than its nominal size; fittings are even bigger....

page 24 of this manual ( ) has the OD of a 3" ABS Schedule 40 DWV pipe at 3.5", but I'd strongly recommend consulting the manufacturer of the pipe or fitting that you're using, or a good set of calipers to measure it before you buy a new holesaw, much less drill that hole!

be patient! be careful! good luck!
Joseph & Gabrielle

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Old 07-11-2010, 04:07 PM   #3
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1979 31' Sovereign
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I was under the impression that those fittings were "spin welded"..
See our blog here on how two RV/AS rookies tackle a 1979 Sovereign resto!!

Just the photos.. (sometimes you don't need the blog, just a picture worth a thousand words..)

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Old 07-11-2010, 04:11 PM   #4
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1976 25' Caravanner
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Campton , New Hampshire
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Before you cut any holes you might want to find a plastics shop . Usually those fittings are spun welded into the tank. Not sure what you have for fittings perhaps they are something different , you didn't say .
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Old 07-11-2010, 05:24 PM   #5
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1968 24' Tradewind
Oxford, , Mississippi
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I'm assuming you put the new black tank into position under the trailer and then marked the top through the hole in the floor. I installed a new tank in my Trade Wind. At first I just measured the old one and marked the new tank because it was the same. After thinking about it, I decided to mount the tank in the galvanized box and raise it into position under the trailer. Glad I did, because I would have made a big mistake as the hole would have been nearly 2 inches off. My new tank is fiberglass so I just glassed the flange supplied with the tank into position after cutting the hole. Can't give advise as to how to attach stuff to your tank, but having it in the exact right position is job one.
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Old 07-11-2010, 05:42 PM   #6
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1973 27' Overlander
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Trying to remember how I did mine, seems like on the fitting was a small lip that went inside tank,if so you just need a hole saw that size and glue it in.If not the 31/8 will work fine,remember the fitting has a stop in it,so you should be good. Dave
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Old 07-11-2010, 05:46 PM   #7
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1966 22' Safari
Davis City , Iowa
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New plan

After reading the responses to my query, I am going to first call the company I bought this tank from to see what they say. Then I'm going to find someone to cut the hole and place the flange in correctly. Thanks for your help.
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Old 07-12-2010, 09:06 AM   #8
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Columbia , South Carolina
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Mark the OD of the flange over the existing hole and enlarge it with a jigsaw or a dremel tool. If you have a black plastic ABS tank, use ABS glue or ABS shavings mixed with acetone to form a solvent paste (that will also patch a hole).
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Old 07-12-2010, 10:18 AM   #9
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1977 Argosy 24
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Black ABS fittings glue to Black ABS tanks and pipe. Like it was said above, acetone and ABS shavings is what the glue is made of. Cut the hole the same size as the hole in the fitting, unless the fitting has a lip on it to center it in the hole.
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Old 07-12-2010, 12:34 PM   #10
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2000 30' Limited
battle ground, , Washington
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abs spin welding?

okay you guys, what the heck is this procedure?
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Old 07-12-2010, 01:07 PM   #11
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South of the river , Minnesota
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Spin welding - Wikipedia, the free encyclopedia

ABS is easy to cement and you can get ABS cement in any hardware store or home center. That's what I would do.
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