Missouri Drainlayer License

Why Plumbers Need a Separate Drainlayer Credential

Most plumbers in Missouri assume their trade card covers all pipe work on a property. It doesn't. Under RSMo § 341.170, sewer work outside the building envelope — connecting to public mains, installing exterior sewer lines, and extending drainage systems beyond a structure's foundation — requires a separate Master Drainlayer license. A general plumbing license, whether journeyman or master, does not authorize exterior sewer installations.

This distinction catches contractors off guard, especially when a residential project includes a sewer lateral replacement or a new tap into the municipal system. If you pull a plumbing permit for interior work but the scope extends outside the building footprint, you need the drainlayer credential to stay legal.

How the License Works in St. Louis County

St. Louis County is the jurisdiction where the drainlayer license comes up most often because the county's Board of Plumber and Drainlayer Examiners explicitly administers both credentials. The board name itself signals the regulatory separation — plumbing and drainlaying are treated as distinct disciplines.

To obtain a drainlayer license in St. Louis County, you must register with the board through the Accela portal. The application process runs parallel to the plumbing license: follow the board's requirements for experience documentation, any required examination, a compliance bond, and liability insurance.

St. Louis City's Board of Examiners of Plumbers and Drainlayers operates under the same dual-credential structure. The city maintains separate application tracks and bonds for each license type.

Bonds and Insurance for Drainlayers

Drainlayer licenses carry their own financial requirements distinct from the plumbing contractor bond. In St. Charles City, drainlayer applicants must post a separate $10,000 compliance bond specific to drainlaying work, on top of whatever plumbing contractor bond they already hold.

The surety bond must name the local political subdivision as the obligee and be signed by a licensed corporate surety, just like the plumbing bond. Insurance requirements (general liability and workers' compensation) apply to the contracting business. If you hold dual licenses, confirm with the local authority and your insurer how the certificate must cover both scopes of work.

When You Need It and When You Don't

The drainlayer license is required for installing or replacing sewer laterals from the building to the main, making new taps into public sewer systems, and extending exterior drainage lines.

Interior drain, waste, and vent (DWV) work stays under the standard plumbing license. The dividing line for sewer and drainage work is the building envelope — once that work crosses outside the foundation or slab, drainlayer authority takes over.

Not every Missouri jurisdiction enforces this separation with the same rigor. Smaller cities may fold exterior sewer work under the general plumbing contractor license. In the St. Louis metro area and other jurisdictions covered by RSMo § 341.170, check the local board's rules before assuming exterior sewer work is covered by a general plumbing credential.

Get the Full Credential Map

The Missouri Plumber License Guide details the plumber-drainlayer split across every major jurisdiction, including which boards issue both credentials, what additional bonds are required, and how to register for drainlayer exams in St. Louis City and St. Louis County.

See more Missouri guides →