The short version
- Your part
- Usually the building drain inside the house plus the service lateral out to the public main
- Public part
- Usually the main in the street or alley easement, maintained by the sewer provider
- Who to ask
- The provider named on your water and sewer bill; in most of the city that is the City of Thornton utilities department
- Grey zone
- The connection point (the tap or wye) and any section under a public street; rules vary, so ask before digging
Why the split matters during a backup
When sewage rises out of a basement floor drain, the first practical question is whether the blockage sits in your own line or in the public main. If the main is plugged, every house upstream of the blockage on that main is pushing wastewater toward the same obstruction, and the lowest drains on the street overflow first. If your lateral is plugged, only your fixtures are affected, and the fix is a plumber with a cable machine or a hydro-jetter.
In most Front Range cities, including Thornton as described on the homepage, the property owner is responsible for the service line all the way to where it joins the main. That surprises people because the lateral runs under the front yard, sometimes under the sidewalk and occasionally under part of the street. Being under public land does not automatically make it public pipe. The exact boundary is set by the provider's rules, which is why the bill matters: a handful of north metro neighborhoods are served by water and sanitation districts rather than a city, and each district writes its own policies.
Typical responsibility by section
| Section of pipe | Usually maintained by | What to check |
|---|---|---|
| Fixtures, traps and floor drains | Owner | Dry traps, missing drain covers, old standpipe connections |
| Building drain under the slab | Owner | Cracks, offsets and belly sags show up on a camera |
| Cleanout and lateral under the yard | Owner | Roots, separated joints, crushed sections |
| Lateral under sidewalk or street | Often owner; ask | Whether a right-of-way permit is needed to excavate |
| Tap at the main | Varies by provider | Who repairs a broken connection |
| Public main | Sewer provider | Report blockages; do not attempt to clear it yourself |
Whose problem is it right now?
Use what you can observe in the first hour to point the call in the right direction.
- IfOnly your house is backing up and neighbors are fineThenTreat it as a private lateral problem first. Stop using water and get a plumber to clear the line from your cleanout.
- IfSeveral homes on the block report sewage at the same timeThenCall the sewer provider's after-hours line on your bill and report a possible main blockage. Keep a record of the time you called.
- IfThe plumber clears your line but finds no blockage in itThenAsk the plumber to note that in writing; it supports a report that the issue was in the main or at the tap.
- IfA camera shows the lateral broken under the streetThenAsk the provider and the city about permits and responsibility before any excavation is scheduled.
Common questions
How do I find my cleanout?
Look for a capped pipe a few inches across, usually in the yard between the house and the street or near the foundation, sometimes inside the basement near where the line exits. Newer homes often have one outside; older homes may not.
Can the city camera my lateral for me?
Providers generally inspect their own mains, not private laterals. Ask your provider what they offer; a private plumber with a sewer camera is the usual route.
General information for Thornton, not a quote or professional advice. In an emergency, call 911.