Author Options:

How to seal unused drain pipe? Answered

The short version:

I have an old PVC sewer drain pipe that comes up out of a concrete slab floor.  Under the floor, the other end of the pipe connects to other drain pipes in the house, so before I cover the area with more carpeting, I'd like to seal that pipe off permanently to avoid any possible leakage in the future.  I'd like to avoid disturbing the concrete floor, if possible.  I'd like to put some kind of plug in the pipe and glue it into place with common PVC primer and cement, but I don't know if there's any kind of plug made for this purpose.

Any suggestions?

The details:

I've taken down a non-load-bearing wall in my house.  The wall used to carry pipes for water (coming down from the second floor above), natural gas (embedded in the concrete slab floor), and sewer (also embedded in the slab).  These were all used for a poorly-positioned laundry room.  I've easily sealed the copper pipes for the water and natural gas, but I'm left wondering what to do with this two-inch sewer drain pipe.

At first, I thought of covering it with a PVC cap, but to do that, I would need to chip away part of the concrete floor far enough down so the cap wouldn't be above the floor surface.  I would also need to be careful not to break the pipe as I chipped away the concrete.  If I were successful with that and then glued a cap on at the right height, then I would need to fill the space around it with a small amount of concrete.  Besides not wanting to damage the pipe, I'm sure I'd make a real mess of the carpet nearby.

Then, I thought, rather than gluing a cap over the *outside* of the pipe, maybe there's some kind of cap that I can glue on the *inside* of it istead.  However, I don't know of any such pipe fitting.  It seems that all the home improvement stores around here sell fittings that go on the outside of the pipe.  So I'm looking for creative ways to plug up the end of this pipe.

The other end of this pipe connects to other sewer pipes in the house that are currently in use.  I thought of possibly pouring a cement-like substance into the pipe to seal it, but I can't guarantee that it wouldn't go into the rest of the system and cause a disastrous plug for the whole thing.

PS:  Excuse the orientation of the photos I've attached to this posting.  They looked fine on my phone, but when I upload them to Instructables, the site insists on rotating them.

PPS: I do plan to cut the PVC pipe off even with the floor just before sealing it.  I'll use my trusty Dremel Multi-Max for that.



Thanks to suggestions from caitlinsdad, I found the right product for the job.

The Oatey expandable plug with wingnut would have left too much above the floor when it was in place. I expected the next smaller size might have fit inside the two-inch pipe enough to put everything below the floor surface, but it was still to wide. The PVC plug I found was made to fit inside a two-inch fitting, not the pipe, so it was not a solution.

Finally, while at the Home Depot, an employee suggested this Oatey inset knockout test cap:


It's PVC so it can be glued to the pipe and it has a thin shoulder so it won't appear much above the floor. It cost only $0.31 USD. The HD guy had forgotten about this item until I asked about the one that caitlinsdad suggested. It's not easy to find this item on the HD website because there are so many caps available. Sorting by size is a text search rather than using product specifications. Also, this item is called an "inset" cap, but the geniuses at HD labelled some of them "insert" on their website, which can make them harr to find, too.

As the photo of the end product shows, after I cut the pipe flush with the floor, I glued in this new cap. I then used a sander to reduce its profile and get it as close to the floor surface as possible. I cut off part of the pull tab, too, just to make sure that wouldn't get in the way. I think to finish the job off, I may fill in the recessed part of the plug with expanding foam or glue a small square of sheet metal over it.

Thanks for all the suggestions!



Get a cleanout or expandable test plug that fits. If the top of the plug still sticks out above the floor, you can get an internal pvc pipe cutter which is like a rotary dremel circular saw blade on a drill shaft. Slice off a bit of the top of the pipe embedded in the floor. You could also probably chip it out with a knife/sharp chisel. Good luck.

For a couple of bucks and a trip to home depot, it doesn't hurt to get one to test fit. It would seal it permanently when you glue it in.

But being a drain pipe, I think I would want to try to seal as deep in the pipe as possible near the joint when it Ts or connects to the main pipe. I'm guessing you can't get under the slab or no basement under access but you would still leave a column of built up waste gases that would not get flushed out with use - hence why p-traps connected. You could probe to see how far the pipe goes and fashion a plug from tinfoil. Attach a string or wire to push it in to depth and fill it up with the spray foam - use the less expanding stuff for doors and windows so it doesn't push the plug in further.

If you are worried about concrete getting into the plumbing, force ball of aluminum foil tightly onto the pipe few inches down then top it off with grout or concrete. A Styrofoam ball may work too.

I usually fix those problems the easy way:
Push a bit of paper down the pipe then a nice blob of expanda foam -the stuff that comes in a can ;)
Cut the excess off once cured and job's done.
If you ever need the pipe again you can still remove the foam with a saw blade or thin knife.

if it elbows close to the surface you could fill it with silicon bathtub sealant

From what you described, the pipe's orientation is going 'down' through the floor into the sewers? Right?

I think I'd just get a wooden dowel (or cut some block of wood down) so that it either sticks all by it self and has to be (lightly) hammered into the pipe or is a little bit smaller than the inside of the pipe. In the latter case I'd screw another piece of wood to it to form a T structure and glue the piece in with a) thick resin or b) just silicon. Once it is set, remove the T handle and cut it flush to the floor. Silicon would be a good sealant in any case.