The ideal drain pipe slope is 1/4” per foot, which is also the minimum per code for pipes 2-1/2” diameter or less. This incline allows the water to move slowly enough to float the solids along with it, and fast enough to scour the pipe walls. But when a pipe is sloped too steeply (1/2” per foot or more), it is just as likely to clog as an undersloped pipe because the liquids travel too fast and the solids get left behind. No maximum slope is specified in the International Plumbing Code (IPC) table, shown below, but it is definitely a practical consideration.
“In some cases a little extra slope can’t be avoided, and there is actually a lot of debate on this subject,” according to plumber James Freeman, of J.W. Freeman Plumbing. “Some people think that the 'too much slope' problem is a plumbing myth, while others think it’s very important."
Also, see our blog post What is the minimum and maximum slope of the trap arm of a plumbing drain?
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Here’s links to a collection of our other blog posts about PLUMBING PIPES:
• How can I protect my pipes to keep them from bursting during a hard winter freeze in North Florida?
• Can galvanized steel pipe still be used for new water lines in a house?
• How can I tell if I have cast iron pipes in my house?
• Why can't a sanitary tee be used for a horizontal-to-horizontal drain pipe connection?
• What is the difference between green and white sewer drain pipes?
• Is a washing machine drain hose required to be secured at the standpipe?
• What are the abandoned pipes sticking out of the wall in my house?
• What are the code requirements for plumbing vent terminations?
• What are the code requirements for layout of drain piping under sinks?
• What causes a gurgling sound when a bathtub or sink drains?
• What is a "combination waste and vent" in a plumbing system?
• What is a building trap?
• What is a galvanized nipple?
• What are the pipes sticking out near my water valves?
• How do you accurately find a broken water pipe leak under the floor slab?
• What is the difference between water pipe and sewage (waste) pipe?
• Are plastic pipes (PVC, CPVC, and PEX) safe for drinking water?
• Is a hot water faucet handle required to be on the left?
• What's that powdery crust on the pipe connections at the water heater?
• If all the plumbing drains have water in them and you can still smell sewer gas, what's causing the problem?
• How can I tell what type of plumbing pipe I have?
• Why is there a flexible accordion pipe under the sink?
• What is the difference between PVC and ABS plumbing pipe?
• What is the difference between water service pipe and water supply pipe?
• What are the pipes on my roof?
• How can I find out what type of water pipe runs underground from the water meter to the house (service pipe)?
• What is a P-trap?
• Why is old galvanized steel water pipe a problem for homebuyers?
• What does polybutylene pipe look like? Why is it a problem?
• Which water pipes are an insurance problem and possibly uninsurable?
• Can you connect CPVC pipe directly to a gas water heater?
Visit our PLUMBING page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.