Repairing Brass Threads In A Floor Sewer Washout Plug

[Cobra]

Obviously cannot see it but would the thread on the floor be just damaged along the top edge?
If that is the case, the idea of using a Dremel with either a cut off wheel or a burr to remove the uppermost thread might allow the starting of the plug.
Otherwise I would be temped to make up a wood or plastic plug that would fit just inside the threads and silicone or epoxy it in.

 

[intjonmiller]

Okay, here's what we're working with. Apologies if the Tapatalk image error means you can't see it. I'll try to get to a computer to upload them directly as well, but I just disassembled my main computer so I could move the desk it sits on and get these pictures.

The first image is just for context, showing how much room we have to work with, since the other is too close to make sense of anything but the thread.









As you can see, there is room for a reasonable handle. And it turns out this side is steel, not brass like the plug. I hadn't remembered that. Last time I ran a synthetic "wire brush" drill attachment that fit just right in the opening, to try to clean out the threads, to no avail. I don't think there's much left of the threads to be able to repair them.

I'm headed out to look for another replacement expanding plug. Let me know if you think brazing or soldering would seem doable (after a lot more cleanup) in case I come up empty.

 

[John Hasler]

This is probably an odd question for a machinist forum, but we have such a broad range of professions and experiences covered in this community that I can't think of a better place to ask this. First the requisite background info...

I'm renting a home. Last February the sewer backed up, flooding the basement bathroom and my home office. The final sewer washout location in the home is, for some reason, in the floor of that office. The plumber who came and snaked all the way out the foundation and to the city's line (retrieving an impressive rootball in the process) used that washout for that job, because the screwy plumbing didn't line up right to let him use the open toilet drain instead. In the process the threads of the old brass fitting were damaged, so after he left and I cleaned up the filthy residue I was unable to replace the plug because I couldn't get the thread to start.

It's an odd size plug. 3.5"? Something like that. The plumbing supply place didn't have a universal plug (the expanding rubber variety) that fit (1950s construction). The landlord bought the closest size and I added a couple coils of thin rubber sheeting to increase the size, thinking that once it was expanded in place it would form a good enough seal for that low pressure drain pipe application.

I was wrong. There is now a puddle right there.

View attachment 138910

I'm taking the day off work to get my office moved out, once again remove the carpet and pad, and all that. The plumber and I both recommended that the line be scoped last time and the landlord cheaped out. I will insist this time, as this is becoming a serious problem. It's almost certainly a broken sewer line in the yard. Just saying because I'm confident that the knowledgeable and helpful people of this forum would encourage me to get it scoped, and I don't want that part of this to distract from the real question:

How do I fix the threads so I can put the brass plug back in?

Even if a tap for that size exists, there's no way he will pay for it. Since it's not a size that can be found readily at plumbing supply places I'm confident the mechanical contractors I could call won't have one. And the fitting is buried in the cement, so the lathe is not an option.

What are my options? I'm wondering about maybe brazing in a new fitting in a slightly smaller but standard size, within the old one. Other than the fact that it is wet and dirty (frustrating but manageable challenge) do you see any reason why that wouldn't work?

Any other ideas?

Press or glue in a plastic reducer to take either the largest plug you can buy or the existing one after you turn it down and re-thread it?

Drive anchors into the concrete around the opening and then bolt a gasketed plate down over the opening?

 

[Billh50]

Look for one of these http://www.petersenproducts.com/143-1_pipe_plug.aspx

 

[12bolts]

Plug the pipe with newspaper and put a thin layer of grout in. Let that set up, then fill it flush to slab level with more grout. Mark a circle where the approximate centre of the pipe is for the next plumber to find. No leaks or odours.
Thats how plumbers seal pipes, septics, etc
edit Based on your measurement of the plug thats most likely a 3" NPT fitting

Cheers Phil

 

[RJSakowski]

Take a look at this plug. https://www.zoro.com/cherne-industries-pipe-plug-mechanical-3-in-natural-rubber-269921/i/G3234296/
Usually, this type of plug uses two opposing conical pieces to expand the rubber when the nut is tightened. If there isn't enough range, you can trim the tops of the cones which will allow you to draw them closer together, increasing the diameter.

Be aware that aside from the backflow of sewerage, there is lokely a possibility of sewer gases buildup. Sewer gas is explosive and can be toxic so you need to make sure you get a good seal.

 

[intjonmiller]

Again, a 3" expanding rubber plug doesn't fit. I just went to three plumbing supply places, with my cap in hand, and they were all confused by it. They don't have a cast iron solution, at least not in a size slightly smaller than this (had to drop all the way to 2", which is not large enough for me to fit in this in any way except dropping it down the hole), so I may need to look at pvc and JB weld.

At the last store I did pick up a new brass plug (nominally 3", so you would think the expanding type would work, but they don't) figuring the cleaner, sharper, slightly larger thread might engage. It did. But even with thread tape and really cranking on it I can't get it to seal enough to not bubble when I flush the toilet.

 

[intjonmiller]

I take it back. I wrapped it with thread tape five times. It was very difficult to get it to start threading on but it finally did and even with less torque it seems to be sealing. I'm satisfied with that.

 

[Billh50]

From looking at the photos. there only seems to be 2 or 3 good threads i the pipe. That alone would not make a good seal. So from what I see only 2 things will work.
1) Tear up the floor and replace the pipes
2) One of the rubber expansion plugs in the link I posted.

I think the plug would be the least expensive route.

 

[4GSR]

I can get a 3-1/2" or 4" bridge plug to set in that pipe ID, set it in place. Guaranteed not to leak. Will hold 10K psi. May split the cast iron pipe when set. Have to be drilled out with a PDC bit. Have to bring in a workover rig.