Annapolis, Md. ? 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, but the biggest problems are caused by grease and cooking oil that Thanksgiving chefs pour down the garbage disposal.

The days after Thanksgiving can pay off especially big for plumbers, and the long weekend can bring an extra $500,000 in revenue, 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.”