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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?

  • Hello, and welcome to Stack Exchange. I'm assuming the answer is going to be "it depends". What are you pouring down; canola oil or bacon grease? How large and how cold are the drain pipes? Do you habitually run hot water down the drain? – Daniel Griscom Apr 11 '18 at 18:45
  • Thank you, let's assume the pipes are standard,1.5" in diameter, and the grease is something like bacon grease. TBH I just poured a little bacon grease down my sink accidentally this morning, and I'm trying to judge how likely I'm going to be to have to take the sink apart when I get home from work. – jdoejdoe Apr 11 '18 at 18:55
  • Since this probably isn't the first time you have done it, then I would ask what has happened in the past when this happens? This question should attract some good answers. – SDsolar Apr 12 '18 at 6:14
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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.

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  • One of the suggestions I have heard is to make sure the fat has solidified before putting it down the drain and to follow that up with cold, not hot, water. Then again, if it's solidified, it's relatively easy to scrape it out and get rid of it with the regular garbage. – SteveSh Jan 5 at 0:42
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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.

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  • even solids will eventually mover down sewer pipes, if you don't make a habit of throwing all the grease from your bacon and 85% burger down there. You wash your hands after gardening, and rocks get down there. If you don't put too much in, your sewer pipe can handle it. – Wayfaring Stranger Apr 12 '18 at 2:38

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