# MSD 2027 Rules: Mixed-Use Laterals & Grease Lines | Legacy > MSD's 2027 draft spells out a separate commercial grease line lateral to the interceptor in mixed-use buildings. What changes and how to plan the plumbing. Canonical: https://legacyplumbingmo.com/resources/msd-2027-mixed-use-laterals-grease-interceptors Last updated: 2026-11-09 [Resources](https://legacyplumbingmo.com/resources) Compliance MSD's 2027 draft spells out a separate commercial grease line lateral to the interceptor in mixed-use buildings. What changes and how to plan the plumbing. November 9, 2026 6 min read Written and reviewed by the Legacy Plumbing field & estimating team Updated November 9, 2026 · Legacy Plumbing is a union commercial plumbing contractor serving St. Louis since 1996. Rule status, checked November 9, 2026: MSD's website still labels the 2027 Rules and Regulations and Engineering Design Requirements a draft (dated July 1, 2026). MSD posted its responses to public comment on October 15, 2026, and its proposed schedule applies the 2027 rules to plans first submitted on or after January 1, 2027; plans submitted earlier stay under the 2018 rules. Section numbers here come from the draft and could change in the final version. In a mixed-use building, MSD's 2027 rules expect each "use-section" to have its own sanitary lateral, and the draft now names a separate commercial grease line lateral flowing to the [grease interceptor](https://legacyplumbingmo.com/facility-services/grease-trap-cleaning) as one of them. For a ground-floor [restaurant](https://legacyplumbingmo.com/industries/restaurants-food-service) under apartments, that means three lines leaving the building: the commercial sanitary lateral, the commercial grease line to the interceptor, and the residential lateral. They may join on private property outside the building, downstream of any external grease trap or sampling point. Legacy Plumbing is a union commercial plumbing contractor that plumbs restaurant and [multifamily](https://legacyplumbingmo.com/industries/multifamily) buildings and cleans grease interceptors across the St. Louis metro. Your engineer, the plumbing code official and MSD decide what your building needs. ## What the 2027 draft says Section 3.030.09, item 17 ("Lateral for Commercial Use"): for mixed-use buildings, such as commercial on lower floors with residential above, separate sanitary laterals shall be provided for each use-section. The example in the 2027 draft lists a commercial sanitary lateral, a separate commercial grease line lateral flowing to the grease interceptor, and a separate residential lateral; the grease line is new wording in the draft. The use-section laterals may be connected together on private property outside the building limits and downstream of any external grease traps or sampling appurtenance. The rules on common laterals carry forward: a common lateral is allowed only for a building of the same use or vertically stacked condominiums. Side-by-side units each need their own lateral connected directly to a public sewer, and freestanding commercial leaseholds that could become outlots must be connected directly and separately to a public sewer. ## Grease interceptor rules that carry forward The draft keeps MSD's interceptor language: - If MSD requires it, grease, oil and sand interceptors must be provided where needed to handle wastes containing grease or oil in excessive amounts, flammable wastes, sand or other harmful materials. They are not required for private dwelling units. - Drawings and specifications must be submitted to MSD for approval before any interceptor is installed. - Interceptors must be located so they are readily accessible for cleaning and visual inspection on the influent and effluent sides. - Design and permitting follow local plumbing codes, and discharges must stay within Sewer Use Ordinance limits and prohibitions. - Grease and oil interceptors must be watertight, built of impervious materials that handle sudden temperature changes, with removable covers that are gas-tight and watertight when bolted down, unless MSD approves otherwise. - All interceptors must be kept in effective operation at all times, by and at the expense of the user. For maintenance, MSD directs food service facilities to clean grease interceptors at regular intervals and when they reach 60 percent of capacity. See our [grease trap cleaning](https://legacyplumbingmo.com/facility-services/grease-trap-cleaning) page. ## Planning a mixed-use or restaurant build-out - **Separate the waste streams inside the building.** Route kitchen grease waste to its own line and interceptor, apart from restrooms and residential stacks. - **Pick the interceptor location for access.** MSD wants both sides open for cleaning and inspection, so keep it out from under racking, parking stalls that are always occupied, or tight closets. - **Plan where the laterals join.** Any connection between use-section laterals happens outside the building and downstream of external grease traps or sampling points. Coordinate that point with the site utility contractor; our sister company [Kuesel](https://kueselinc.com/services/sanitary-sewer) builds site sanitary work. - **Submit interceptor drawings early.** MSD approval is required before installation. - **Check basement fixtures.** New buildings also need strapped plumbing for basement-level fixtures under the 2027 draft; see [strapped plumbing and MSD's 2027 rules](https://legacyplumbingmo.com/resources/msd-2027-strapped-plumbing-requirements) . - **Plan for camera inspection.** A camera run before turnover documents the new laterals; our sister company GreenFlow Solutions explains [what MSD's 2027 rules mean for laterals and maintenance access](https://stldrain.com/blog/msd-2027-rules-sewer-laterals-maintenance-access) . Legacy Plumbing works on [restaurant and food service](https://legacyplumbingmo.com/industries/restaurants-food-service) and [multifamily](https://legacyplumbingmo.com/industries/multifamily) projects, from [tenant finish](https://legacyplumbingmo.com/commercial/tenant-finish) to [new construction](https://legacyplumbingmo.com/services/new-construction) . Call 636-978-0120, Monday through Friday, 7:00 AM to 4:00 PM. General information from a plumbing contractor, not engineering or legal advice. Your engineer, the plumbing code authority having jurisdiction and MSD set the requirements for your project. ## FAQ ### Does a mixed-use building need separate sewer laterals under MSD's rules? Yes. MSD's 2027 draft requires separate sanitary laterals for each use-section of a mixed-use building, for example a commercial sanitary lateral, a separate commercial grease line lateral to the grease interceptor, and a residential lateral. ### Where can the laterals from different uses connect? On private property outside the building limits, downstream of any external grease traps or sampling point. ### Does MSD have to approve a grease interceptor before it is installed? Yes. MSD's rules require drawings and specifications to be submitted to MSD for approval before any interceptor is installed. Design and permitting follow local plumbing codes. ### When should a grease interceptor be cleaned? MSD directs food service facilities to clean grease interceptors at regular intervals and when they reach 60 percent of capacity. ## Sources - [MSD, Rules, Regulations & Design Requirements](https://msdprojectclear.org/doing-business/development-review/rules-regulations-design-requirements/) - [2027 draft redline (section 3.030.09, items 9–17)](https://portal.laserfiche.com/Portal/DocView.aspx?id=9591989&repo=r-a96260ce) - [MSD responses to comments (Oct 15, 2026)](https://portal.laserfiche.com/Portal/DocView.aspx?id=9676505&repo=r-a96260ce) ## Related services & projects - [Service areas](https://legacyplumbingmo.com/service-areas) - [Restaurant Plumbing in Crestwood (Crestwood, St. Louis County)](https://legacyplumbingmo.com/projects/restaurant-plumbing-crestwood-mo) - [Ground-Up Site Utilities (O'Fallon, MO)](https://legacyplumbingmo.com/projects/ground-up-site-utilities-ofallon-mo) - [Plant Cafeteria Plumbing in St. Louis (St. Louis, City of St. Louis)](https://legacyplumbingmo.com/projects/pharmaceutical-plant-cafeteria-renovation-st-louis) - [Commercial Plumbing Permits and Inspections in St. Louis City, St. Louis County and St. Charles County](https://legacyplumbingmo.com/resources/commercial-plumbing-permits-st-louis-st-charles) Service Area Commercial Plumbing in St. Louis, MO See local coverage ## Talk to a St. Louis commercial plumber Call 636-978-0120, Monday through Friday, 7:00 AM to 4:00 PM. [Contact Us](https://legacyplumbingmo.com/contact-us) ## More Resources - [Grease Interceptor vs. Grease Trap: Choosing, Sizing and Placing One on a St. Louis Restaurant Build-Out](https://legacyplumbingmo.com/resources/grease-interceptor-vs-grease-trap-st-louis-restaurant-build-out) Hydromechanical or gravity? How St. Louis City, St. Louis County and St. Charles County codes size grease interceptors, and what to settle before slab cuts. - [Legionella Water Management Plans: The Plumbing Side, Explained for St. Louis Facility Teams](https://legacyplumbingmo.com/resources/legionella-water-management-plan-plumbing-st-louis) What a Legionella water management plan covers, who needs one, and the plumbing work behind it: water heaters, mixing valves, recirc loops and dead legs. - [Strapped Plumbing and MSD's 2027 Rules: What St. Louis Building Owners and Builders Need to Know](https://legacyplumbingmo.com/resources/msd-2027-strapped-plumbing-requirements) MSD's 2027 draft requires strapped plumbing for basement fixtures in all new buildings. What it is, what's allowed elsewhere, and how to plan for it. ## Need a Plumber in St. Louis or the Surrounding Area? Call 636-978-0120, Monday through Friday, 7:00 AM to 4:00 PM. [Get Free Estimate](https://legacyplumbingmo.com/contact-us) ## Related - [Contact Legacy Plumbing](https://legacyplumbingmo.com/contact-us) - [Company facts](https://legacyplumbingmo.com/company-facts) - [All pages (llms.txt)](https://legacyplumbingmo.com/llms.txt)