What is the minimum drainage slope for a sewer pipe?

Drainage slope is essential for proper wastewater flow. According to the Quebec Plumbing Code:

• Minimum slope: 1/4 in per foot (2%) for pipes 4 in and smaller
• Minimum slope: 1/8 in per foot (1%) for pipes 5 in and larger
• Maximum slope: 1 in per foot (8%) for all pipes (beyond this, water flows too fast and solids are not carried along)

Example: A 3 in pipe over a length of 12 feet (3.66 m) must have a minimum slope of 12 × ¼ = 3 inches (7.6 cm) total drop.

Consequences of inadequate slope:

• Insufficient slope: blockages, backups, solid accumulation
• Excessive slope: water leaves solids behind, causing clogs
• Reverse slope: completely prohibited — water must always flow toward the sewer