How much grease accidentally going down a drain is a concern?

Question

I always try to dispose of my cooking grease safely, but I'm curious as to how grease actually causes a clog in a drain. For example, if a bit of cooking grease gets down the drain one time, will it expand and clog the drain almost instantaneously? Or does clogging a drain with grease require repeated abuse / grease and oil constantly being run down the drain?

Edit: Let's assume the grease is a small amount of bacon grease (>1/8 cup), and the pipes are standard 1.5" in diameter pipes. If accidentally poured down the drain in the morning, what are the odds it would stop up the whole drain?

Answer 1

In general, a one-time slip-up dumping grease down the sink won't cause any clogs. Grease creates clogs over time, by building up layer upon layer inside the pipe until water cannot pass through (easily) anymore.

This is most usually a problem with greases that are solid at room temperature but liquid at cooking temperature (or under hot water). When hot, it is liquid enough to be poured down a drain, but very soon after (i.e., while still in the pipes) it cools enough to solidify. It does this on the walls of your pipes. Cooling rates aren't uniform, so the grease doesn't always cool off and solidify into your pipes at the same place each time you pour it down the sink. Over time, enough eventually builds up to cause a blockage. Very similar to plaque building up on your artery walls and causing a heart attack.

Any kind of improper slope of your drain can exacerbate this, and cause the buildup to occur faster. A lot of bends in the pipes, excessively cold pipes, or debris in the pipes could accelerate this as well.

Running hot water down the drain will only push the problem further down the line, as you'll still have the problem of the grease (and water) cooling and solidifying.

Answer 2

Boils down to two simple questions.

1. What is the temperature inside the sewer pipe?

2. At what temperature does this particular grease become solid?

If the "temperature of the sewer pipe" is below the "becomes solid" temperature, what happens next is inevitable. And the question is whether it will accumulate enough to block the pipe.

Underground temps are typically 30-60 degrees F. Sewer lines are ideally built below the frostline, but weather extremes of late are moving the frostline.