Retailers are not the only businesses who reap big profits on the day after Thanksgiving — for plumbers, it’s known as Black Friday, too.

 “Our incoming calls for service on that day will jump almost 50 percent,” said Paul Abrams, spokesman for Roto-Rooter, a national plumbing company. “The day after Thanksgiving is just crazy.”

 Clogged drains from plenty of grease and guests are a problem as soon as holiday season starts, but the day after Thanksgiving tops out as one of the plumbing profession’s busiest.

 “We pump out a lot of holiday grease,” said Anthony Haynes, a plumber at First Class Plumbing in Maryland. “The season means there’s a big volume of people getting together to eat.”

 “Clog culprits” include “all the traditionally served items: celery, potato peels, poultry skins and bones, pasta, all the starchy stuff,” Abrams said.

 “It’s the really gooey, sticky stuff that causes problems,” he said.

 The biggest problems are caused by grease and cooking oil that Thanksgiving chefs pour down the garbage disposal. When the grease cools, it solidifies and clogs drains. Roto-Rooter suggests wiping the grease from pots and pans with paper towels and throwing them away in the trash.

 But Haynes said a lot of people do not realize the effect grease can have on pipes. 

 “We try to educate homeowners that it’s (dumping grease) inappropriate to do,” he said.

 But the company still gets — and responds to — emergency calls 24 hours a day, even on Thanksgiving and all throughout the holiday season, he said.

 The days after Thanksgiving can pay off especially big for plumbers.

 Calls to Roto-Rooter from Thanksgiving through Sunday will number between 17,000 and 20,000, and the company will earn an extra $500,000 in revenue, Abrams said. The cost per job varies by region, but could be “anywhere from $65 to a couple hundred bucks, depending on how severe the clog is,” Abrams said.

 Normally, kitchen sink calls make up about 10 percent of the total calls, but during the holiday they will increase to about 20 percent of all calls, Abrams said.

 “Almost all of our service technicians have to work on Black Friday,” Abrams said. “They know not to ask off of work that day.”

 He warned people with slow drains before holiday season that they might want to think about calling a plumber before the guests show up and to avoid a rush and added expenses.

 Warnings aside, people still call even if they have guests arriving in an hour or two, Abrams said.

 “It sounds like they’re calling 911,” he said.