I've got a 1953 single story house with a basement. All the original drain plumbing is cast iron. We've been here about 3 years, and the drains are constantly backing up. Sometimes snaking a drain will open it back up for a while, without ever really pulling out much material.

Sometimes the drain refuses to start flowing again, and I end up taking things apart and it's always a trap or elbow that is filled solid with something black and very hard. I can't do more than scratch the surface with a screwdriver.

This picture shows an elbow that turned a stack as it went below the slab. It's chock-full of hard, black junk (with what appears to be a tiny hole, part of a channel where water was slowly draining): Sawzalled-off pipe showing the clogging

I'm thinking this is most likely rust, although I'm not certain.

At this point, I've replaced a decent portion of the drain plumbing in the house with PVC, and I just had yet another drain back up (kitchen sink into the laundry tub below). I've already replaced that entire stack down to (and one elbow beneath) the slab.

Is the anything I can do to open these drains up besides replacing the pipe? I really am not looking forward to putting other projects on hold to cut up my slab again.

2 Answers 2


You may have a home that the previous owners dumped a lot of cooking grease down the kitchen drain. Over time this can get hard as a rock and get black from mildew and other icky things you don't want to think about.

The pic does not look like rust.

You may need to call a plumber or Drain cleaning specialist. I got to purchase a home rather cheaply because the owner believed the drainfield and septic needed replaced. The drains needed cleaned because of cooking grease. Got that done and no more problems.

  • I've dealt with grease hardened in drains, and I've never had it be this rock solid. Also, it's in all the drains, not just the kitchen. Maybe mineral build-up reacting with the pipes? The water here is quite hard.
    – mister-sir
    Commented Jul 12, 2023 at 1:46
  • 1
    The stuff that came out of the drains were like rocks. I ask if the owner may have poured cement down the drain. The plumber said it was grease. That he saw it get hard like rocks many times. He was using a power snake with some type of heavy metal cutting head.
    – RMDman
    Commented Jul 12, 2023 at 1:59
  • @mister-sir "Also, it's in all the drains, not just the kitchen." If the previous occupants of the house were dumping things they shouldn't have down the kitchen drain, I wouldn't put it past them to dump them down other drains in the house.
    – Dan C
    Commented Jul 12, 2023 at 13:53
  • @mister-sir if the drain going out to the septic tank is narrow like that it would allow grease to back fill into the other pipes as it slowly drains. So, don't overthink which drain it went down it could have easily gotten there via "reflux".
    – Ukko
    Commented Jul 12, 2023 at 16:20

That looks something other than just rust.

Get a drain snake and start drilling. Use different drain snake attachment to clean more. Or if you have to use high pressure washer.

It could be just totally neglected drain with loads of cooking grease.

Use a magnet to test for iron rust.

Some example that look like yours but it is not rust:


Source: https://mtdrain.com/drain-repair-toronto/

Hopefully the previous owner did not pore paint, glue and other stuff during renovations.

  • 1
    A drain snake won't make dent in it. Solid as a rock. It's in all the drains in the house — bathroom, kitchen, etc. Hoping I can find a way to dissolve it or something. Next time I have some accessible, I'll definitely put a magnet to it! Didn't cross my mind last time...
    – mister-sir
    Commented Jul 12, 2023 at 1:42
  • 2
    Rust, Fe2O3 is so weakly magnetic that I don't think you'd even notice the attraction with a everyday ferrite magnet.
    – Travis
    Commented Jul 12, 2023 at 18:19

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