Drain Clean out Plug

The the treads on the drain plug receptacle on our main clean out have become bad. The plug will no longer seal. I have a rubber test plug and TFE dope sealing it now, but what should I do long term? TIA
Pete
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comcast News wrote:

Cast iron w/brass threads, ABS,PVC, Copper ??
There's no reason the expansion plug won't last a long time...
Jim
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comcast News wrote:

take a wire brush and run it into the threads and run the brush around.. this will get all the rust out of the old cast iron fitting.. if this does not work then you can use the tool that is made for this to clear the threads...... you then use the correct plug for it....
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