Old plumbing that won't unscrew

I am trying to get the plug out of an old cast iron drain and it is stuck solid I have tried WD 40 and it didn't work. Someone else suggested CLR but I wanted to check here first. The last think I need is a broken old cast iron drain leaking sewer gas into the house. Any ideas?
Also there is galvanized pipe I need to connect to and they won't come part either.
Please don't tell me this is a case where I have to cut into the old line and make some kind of a joint. It is very hard to reach.
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CLR is gun lubricant, I don't see that working any better than any other oil. Outside of a good penetrating oil and a bigger wrench that's about all there is. I'm sure there's pipe dope all over the threads to that plug and it might as well be concrete by now.
As for the galvanized, same thing, there's probably pipe dope on the threads and when it hardens it's a bitch to remove - plus it's undoubtedly corroded all to heck and that means internally it's semi-welded together. A bigger wrench is the only option I have. May not be the answer you're looking for, but you could try a little further down the line maybe at an elbow or T connection where the pipe is a bit more rigid.
Personally, I use a saws-all and replace it with PEX.
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How to get an old rusted plug out of some plumbing fitting?
Get a good torch: turbo acetylen, propane or close, clear the area around the plug from any combustables, cover the other surfaces; wet them down if you have do; keep water for fire protection on hand ( garden hose from tap).
Heat up the female threaded part real good, apply you wrench (counter clockwise!); repeat if necessary but ensure that pipes are solidly fixed, use two hammers and knock one outside of female thread part while using the other (heavier hammer) as an anvil at 180 degree opposite,move around to cover the circumference. Heat up again( only the female threaded part) Oil and penetrants only work after the sealants are burned out and thread gaps are able to soaked in .
If not successful yet: get somebody stronger, buy a new house, burn down the house if you got good insurance (not), blame the plumber who put it together in the first place!
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I used to do this with brake line fittings that would not come undone. However, propane never worked well because it apparently wasn't hot enough. OxyAcetylene worked real well - heap that puppy until it glows, let it cool, hit it with spray lube, and it comes unscrewed just like that. Not so sure you want to heat your plumbing that hot - might burn down house :P

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On Sat, 8 Jul 2006 16:44:57 -0700, "Matthew Reed" <nospam at zootal dot com nospam> wrote:

Yeah... known by mechanics in the trade as the "red wrench".
--
-john
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On Sat, 8 Jul 2006 16:44:57 -0700, "Matthew Reed" <nospam at zootal dot com nospam> wrote:

If you heat it enough to ignite the sewer gasses, a large flame will shoot out of the vent pipe on the roof. Not too much problem for a cast iron pipe, but if the vent is PVC, call the fire department.
By the way, you cant unscrew an old plumbers wife either......
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On Sat, 8 Jul 2006 16:05:52 -0700, with neither quill nor qualm,

Use http://www.jelmar.com/CLRbath.asp# for plumbing, MiliTec1 for weapons, and Kroil for stuck hardware.
Mulan, try CLR. If it doesn't faze it, dry it and try some Kroil penetrating lube. Also, sometimes it's good to heat the nut with a propane torch. Caution: wooden structures go up quickly.
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Eigenvector wrote:

CLR (Stands for Calcium Lime Rust) is the brand of a hardwater deposit remover. There are better penetrating oils than WD-40.
Heating pipes will soften thread dope and the expansion and contraction when cooling can help loosen rusted pipe..
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Mulan wrote:

WD-40 is not really a penetrating oil. Try using "Liquid Wrench" instead.
Get a longer wrench. Or put a cheater pipe on the one you're using.
Bob
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Mulan wrote:

Heat the pipe and cool the plug. Expansion and contraction does wonders.
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Lots of good ideas from other posters. Stuck and rusty galvanized threaded pipe will nearly always come loose if you can hammer effecitvely around the outer part. You generally need two heavy hammers, one to hold behind the pipe while you hit with the other. As my dad used to say, "Hit it like you mean it!". Light tapping does little good, hit it like you are trying to flatten it. That will stretch the outer part enough to loosen it. The only reasons it will not work are if you can't hit it hard enough or if rust has eaten the pipe too thin to support the threads.
Threaded plugs in cast iron can be loosened similiarly. You hit the center of the plug with a heavy ball peen hammer hard enough to dimple it in and shrink the outside threads. This works really good with the proper brass plugs as they are pretty thin in the center.
In the past, a good plumber would know how to do this and how to judge whether the piping was strong enough to take the pounding. There is some risk of damage and it a judgement call whether it is worth a try.
Don Young
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Thanks everyone, great options to try in the morning. I don't have an oxycetelybe torch or a bunson burner though. I wonder if I can get it hot enough with a gas BBQ lighter? Tomorrow's another fun day! Don Young wrote:

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You can fit a metal water pipe over the handle of a pipe wrench. In one nasty situation, I used two large pipe wrenches and placed 6 ft. long 2" metal pipes over the handles of each.
The 6 ft. long pipes on the wrenches gave me a lot of leverage.
Then I had one person hold one wrench in the counter clockwise direction while I worked the wrench on the adjoining pipe in the opposite direction. Even with all that leverage and pounding with a hammer, it still took a lot of force to get that old water pipe unscrewed!
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I've learned a lot from old plumbers that were faced with this. They drilled a series of holes ~ 1/8" in from the perimeter of a 3 1/4" cast plug that was stuck solid. Cold chiseled the in between material and knocked out that inner circle. From there it is a simple matter to collapse the threaded portion to the inside with a chisel and it drops right out. Easy on the threads too. The post about heating the pipe is good but it will take a good torch to do the job. Use at least MAPP gas or better Oxy MAPP. Richard
Bill wrote:

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