Old Toilet flange with mysterious side stub pipe

[Lee Weinstein]

Leaking water destroying ceiling below toilet in 100-year-old house. Removed toilet and found main pipe has side stub that appears not to be connected to anything (see photo). Looking down stub with mirror, it appears to be capped and cap appears to have hole rotted through. Side stub does not connect to sink drain or anything else as far as I can tell. Side scub visible on left of photo below.

What was such a side stub used for? Can I just plug it?

 

[ExtraMilePlumbing]

I would replace as much of that old pipe as possible.100 years old leaks will start occurring eveywhere

 

[Jamesplumbing06]

That’s called a heel outlet. Yeah it CAN be plugged but the metal that isn’t corroded so far is still the same age as other metal. So you will be right back in a few months. Cut ceiling open and see what you got. Gonna need done anyways. But help out the drywall repair man and cut center of joists with square lines. your wood floor looks a little damaged. So let’s be sure it’s not just the wax seal. Ceiling will need still need to be opened. But don’t invite a plumber in with you diagnoses. He will assume your prepared to go that far and he will jump right in line and never think of wax. Because your idea gets him more cash.