Short answer
A drain line that drips only while water runs through it has a failed joint, and failed joints are repaired. Nothing in a drain is under pressure, so a plumber cuts out the bad fitting, glues or tightens a new one in its place, and tests the run. The pipe either side of it stays. Dry the pipes first, then run one fixture at a time and watch, because several wet joints in one section point at a run that is unsupported and gets rebuilt rather than patched.
Tell one bad joint from a whole bad section
- Dry every pipe and fitting in that area with a rag. Lay dry paper towel under each joint.
- Run one fixture at a time. Flush the toilet, then run the tub, then the sink. Wait a minute after each.
- Watch the joints while the water runs. Drain water is dirty or soapy. Supply water is clear and drips whether anyone uses a fixture or not.
- Mark every joint that has wet paper under it.
- Push up on the pipe next to each wet joint. A run that lifts, droops or swings is carrying its own weight on the fittings.
- Look at what the pipe is joined to. White plastic glued into an older cast iron stack is a transition, and transitions fail on their own.
One wet joint on a pipe that does not move is a single-fitting repair. Two or more wet joints in one section, or a pipe that sags between hangers, means that section gets cut out, rebuilt and re-hung. Water that is clear and drips with every fixture off is a supply leak instead, so shut the water off and get a plumber out today.
Repair or replace
| Situation | What to do |
|---|---|
| One PVC joint drips, pipe is firm and well hung | Repair. The fitting is cut out and a new one glued in, usually inside 2 hours. |
| A metal nut at a toilet or tub drips only in use | Repair. The washer inside that nut has hardened. The nut comes apart and goes back with new parts. |
| Several joints wet in one section | Repair the section. Cut the whole offset run out, glue new fittings, and hang the pipe so no joint carries weight. |
| Plastic drain glued into an old cast iron stack, leaking at the transition | Repair with a shielded coupling at that joint. The cast iron stays. |
| Joints keep leaking again after repairs | Rebuild the run with proper supports. New glue on a pipe that moves fails again. |
| Pipe is buried behind a finished wall or ceiling | Open the wall first. Nobody prices a joint they cannot see. |
| Drip is clear water with every fixture off | Stop. That is a supply line. Shut the water off at the valve and call a plumber now. |
What it costs
Runhome contractor estimates for this job, including the trip and assessment.
| Option | Range |
|---|---|
| Diagnose and repair one leaking pipe or nut at a fixture | $232 to $480 |
| Replace a leaking section of plastic drain with 3 joints, rebuilt and re-hung | $317 to $665 |
Can I do it myself?
Sometimes. One glued plastic fitting on an open basement drain is the friendliest plumbing repair there is, because the line holds no pressure and a mistake drips instead of flooding. You need the right primer and cement, a saw that cuts square, and enough slack in the run to pull the new fitting in without forcing it.
Hire a licensed plumber when the joint is inside a wall or ceiling, when the leak is at a cast iron transition, when more than one joint in the section is wet, or when the pipe needs re-hanging. Some cities, Chicago among them, do not allow homeowner drain work at all and require a licensed plumber on the permit.
What a contractor will ask you
Have these ready and you skip the back-and-forth.
- A wide photo of the whole drain run, showing every wet joint and how the pipe is hung.
- When you first noticed the leak, and whether it is still dripping right now.
- Whether the water is clear like tap water, or dirty and soapy like drain water.
- Which pipe leaked: the white plastic, the older cast iron, or the joint where the two meet.
- Whether one joint drips, or several joints in the same section are wet.
- Whether the leaking fitting sits on a horizontal run or a vertical one.
- Whether you can reach the fitting by hand, or it sits behind other pipes.
- What drains into that line: a bathroom only, or a kitchen or laundry line too.
- Pipe material and size, if the size is printed on the pipe.
Common questions
- Broken water pipe in basement, how bad is it?
Check when it drips. A pipe that leaks only while a fixture runs is a drain, and the leak stops when the water stops. Clear water that drips with everything off is a supply line, and that one gets shut off immediately.
- It leaked before but seems to have stopped now.
A drain leak hides between uses, so it looks cured whenever nobody runs water. Run the fixture above it for 2 minutes and watch the joint. The drip comes back.
- Only when I flush or run the shower or tub does it drip.
That is the drain side, not the supply side. The leak is at the nearest joint above the drip, usually a slip nut or a glued fitting.
- Can a leaking plastic joint be glued over or taped instead of cut out?
No. Glued plastic cannot be re-glued over a leak, and tape on a drain joint buys a few weeks. The fitting comes out.
- I want to get all three connections fixed on white pipes.
Say that at the start. Three leaking joints in one area is priced as one section replacement, not as three repairs, and the plumber brings different materials for it.