I'm trying to cap off an old cast iron pipe that's leaking in our basement.

The pipe used to be connected to a downspout on the outside and to the sewer on the inside, but it's now disconnected on both sides. The downspout was removed, the outdoor side was capped off with some sort of sticky material, and the basement side was left open into the basement.

Here's a picture of the outdoor side:

Partly sealed-off pipe

I'd normally use a worm-drive rubber cap, as shown below, but only half of the pipe is accessible (the rest is hidden beneath the siding, as you can see on the first picture):

Qwik cap

What options do I have to seal off a partly-exposed 4.7in-wide pipe? I'd rather not use concrete, as the outdoor side opens into my neighbors' garden, and I don't want to make a mess there.


Use a two pound maul and break it up. Residential cast iron pipe is rather thin and easily broken. Then repair the siding.

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