Grinder drainage system enables bathroom addition in detached ADU without breaking through concrete slab

Problem

RACELAND, LOUISIANA — When Danny St. Pierre’s daughter returned home from Texas to help care for her elderly grandparents, the family needed to quickly create a comfortable living space. With St. Pierre’s parents, ages 99 and 97, no longer able to remain comfortably in their previous home, the family decided to convert his father’s workshop, a separate structure building from the main house, into a private apartment. The conversion created a detached accessory dwelling unit (ADU), allowing St. Pierre’s daughter and parents to live together in one building with an accessible bathroom.

Adding a bathroom to the detached ADU, however, presented an immediate challenge. According to St. Pierre, connecting the new bathroom to the existing septic tank would have required breaking through a significant amount of concrete to install conventional drainage piping.
In short, traditional gravity drainage was not practical without major disruption, added cost, and extended construction time. The ADU conversion required a solution that could handle waste removal without altering the slab, while still delivering a standard residential bathroom experience for daily use.

Solution

St. Pierre previously worked for Coburn Supply Company, a family-owned wholesaler-distributor of commercial and residential plumbing and HVAC products. As a result, he was familiar with above-floor grinder pump systems and reached out to longtime Coburn sales representative Paul Prouet to explore options.

“I knew they had a product like this, but I had never seen it in action,” he says.

After evaluating the application, St. Pierre and contractor Howard Folse selected the SFA Saniflo Sanibest Pro grinder pump, a heavy-duty grinder system designed to handle a toilet, sink, and tub or shower in full bathroom installations. Its grinding mechanism processes waste before pumping it through small-diameter discharge piping to an existing sewer or septic connection.

Installed directly on top of the existing concrete slab, the compact grinder pump sits behind the rear-discharge toilet included with the Saniflo Sanibest Pro system. Wastewater from the toilet and adjacent lavatory flows into the pump and is discharged approximately 12 feet horizontally to the home’s private septic tank and drain field. The bathtub is not connected to the system.

Although the installation does not require a vertical lift, the small-diameter discharge piping offered a significant advantage. A conventional gravity-drainage system would have required a 4-inch-diameter pipe, resulting in a more disruptive installation and requiring considerably more space. The above-floor system eliminated the need to break through the ADU’s existing concrete slab to install below-floor drainage piping.

Since the detached ADU is located in a rural area, all wastewater is directed to a private septic tank and drain field. The above-floor installation eliminated the need to break through the existing slab to install conventional below-floor drainage piping.

Folse, who also completed the remaining plumbing installation, worked closely with Saniflo’s U.S.-based technical support throughout the process to ensure proper configuration.

“He talked to technical support several times to make sure he was doing it right,” St. Pierre says.

This support helped Folse complete the installation efficiently despite the unconventional layout.

Product Profile: Sanibest Pro Grinder Pump
 

The Sanibest Pro is a heavy-duty, one-horsepower grinder pump system used to install a complete bathroom up to 25 feet below the sewer line or up to 150 feet away from the soil stack. Recommended for restrooms and other commercial/institutional facilities serving the general public, the product has three inlets to handle drainage for a full bathroom: a 4-inch inlet for the toilet connection and a pair of 2-inch inlets, one on either side, to handle gray-water drainage from a sink, a bathtub, or a shower.

The Sanibest Pro is typically shipped with a two-piece toilet that flushes through a horizontal, rear-discharge (above-floor) spigot. Designed to handle sanitary products and other larger items that normally should not be flushed, the powerful grinder pump quickly reduces and discharges effluent to the sewer or a septic tank through a ¾-inch plastic pipe connected to the top of the unit.

Also at the top of the unit is a 1½-inch vent port and a service panel that permits easy service access to all components inside the Sanibest Pro.

Other key features:

Four-year limited warranty

Built-in, backflow-preventing check valves inside the 2-inch inlets for easier installation

Certified by CSA and listed by IAPMO for nationwide compliance

Results

The system has been operating as intended and continues to perform reliably.

“It works well and does exactly what it’s supposed to do,” St. Pierre says.

The completed installation allowed the family to:

• Add a full bathroom to the detached ADU without breaking the concrete slab
• Connect the separate structure to the property’s existing septic system using small-diameter discharge piping
• Complete the project with less disruption and a more efficient installation process
• Create a private, functional ADU that supports multi-generational family care

St. Pierre noted that the system delivers strong flush performance and has proven dependable in everyday use. Technical support was also an important factor in the project’s success.

“Saniflo’s technical support was fabulous,” he says. “Their technical team responded quickly and helped solve the problem.”

Based on his recent experience, St. Pierre sees clear value in using the Sanibest Pro to solve similar application problems where conventional plumbing is not feasible.

“If you want to put something in the middle of the house, that’s the product to use.”