Lazy Daze Owners' Group

Like Larry, I have had good results with JB Weld.  It will be a bit thicker when mixed than the Devcon 2 Ton epoxy.  That will be good for putting it on your finger, then spreading it above the hole, but not as good for penetrating the crack.  I would expect it to do at least as well as the Devcon for holding the crack together, if you can get it in there.  As you will be cleaning/reforming the threads with a tap, don't forget Larry's suggestion to use a saw to open up the crack.  That would make getting the JB Weld in there much easier.  To saw into the crack, a hacksaw blade should do well, using it on the pull stroke.

Ken F in WY

Tedeboy, cleaning the threads - better than a dental pick or mechanic's pick is the pipe thread tap.  It will fit in there and scrape the threads perfectly clean.

I get that you can't easily work your way in there.  So, scrape the threads clean with the tap, something you can do by feel.  Then, take a piece of 100 grit sandpaper, cut a strip 3/8" wide, insert it part way into the hole, then put your finger in, bend the sandpaper over, and use it to scrub the inner surface clean.  Wet a small piece of rag with acetone and wipe that surface clean.  If you can fit both hands in there, use one hand to pull the crack open from above and use the other with a toothbrush and acetone to scrub the crack.  If only one hand will fit, just scrub with the toothbrush. 

When it is dry, you are ready for the JB Weld or epoxy.  With a gloved finger, spread some (a lot, because you do not know the direction or extent of the crack) JB Weld on the inner surface.  Then, if you can get both hands in there, pull on top to open the crack and work more JB Weld into the crack from below.  If only one hand will fit, just spread the JB Weld onto the threads in the hole and run your throw-away pipe in.  With it part way in, wiggle it a bit to open the crack.  Run it the rest of the way in and wiggle.  Remove it, add more JB Weld to the threads and repeat a few times.  Remove the pipe and wipe excess JB Weld with a dry cloth, then let it all cure until it is pretty stiff.  Run the tap in until you feel the resistance change enough to tell you you have cleaned the threads and are starting to cut, then back the tap out.  You can clean the tap with the acetone and a stiff brush.  Let everything sit at least 24 hours, then re-assemble and check for leaks.

Good luck!

Ken F in WY

Tedeboy, cleaning the threads - better than a dental pick or mechanic's pick is the pipe thread tap.  It will fit in there and scrape the threads perfectly clean.

I get that you can't easily work your way in there.  So, scrape the threads clean with the tap, something you can do by feel.  ...,

Good luck!

Ken F in WY

Thinking in terms of prevention, I'm curious as to what may have caused the crack in the threaded area in the first place. Inherent material weakness? "Off-threading"? Overtightening a connection? 

I would still want to open the crack up for cleaning and application of epoxy, the crack needs to be completely clean, if possible.
A short piece of a hack saw blade or a dental pick would still be my choice for removing the crack's dirty plastic.
Ken's description is the same method I would use.

The crack in Ted's tank could have been caused by a too long or unsupported drain pipe, the flexing could have caused the crack to appear and grow.
A protruding drain pipe could have been hit hard enough to crack the fitting.

Larry

Good pic!  That helps.

It looks like the crack extends along the length of the threaded protrusion, but not to the mating of the tank with the fitting.  If so, I would not change any of the plans discussed. I would hesitate to cut open the crack, fearing that I would spread the crack to the tank itself.  If the crack already reaches the tank, nothing to lose in opening the crack.  You might try fitting a small flat bladed screwdriver into the bottom of the crack to spread it, then scrape it clean.  That would also facilitate working JB Weld into the crack. 

Looking at the pic, I think I would add one thing, if possible.  After finishing with the JB Weld, before cleaning the threads with the tap, if there is room, I would try to get a band clamp onto the fixture to hold the crack together, supplementing the strength of the JB Weld work.  I think it will be hard to tighten it ( a whole lot of little turns with a small box wrench), but I think it will add a lot to the strength of the repair.  With the band clamp in place and snugged up, use the tap to clean the threads, then do the assembly.

Ken F in WY

Just remember, pipe taps and threads are tapered. Too much enthusiasm with your tap or the new fitting  would most likely crack something else not too tight, lots of teflon and thread compound help. The hose clamp would be a very good idea if you can do it.

Here's a good pic I took today.

Perhaps something like this:

https://www.homedepot.com/p/ProFlex-Proflex-2-in-x-1-1-4-in-Neoprene-Shielded-Coupling-P3001-2125/205107046?MERCH=REC-_-SearchPLPHorizontal1_rr-_-NA-_-205107046-_-N

if you can find one sized to fit over the fitting at one end, and over the pipe at the other. I have used these several times to mate uncooperative and dissimilar material pipes of different sizes. The rubber coupling inside is sized differently at each end.

Steve