PHOENIX -- It's not just the stores, the lines and the parking lots that get backed up the day after Thanksgiving.

It's also apparently the drains.

Valley plumbers say Black Friday is one of their busiest days of the year.

"(It’s) mostly because of cleaning dishes. The biggest problem in the holiday -- on Thanksgiving -- is the drains stopping up in kitchen sinks. People are putting too much stuff down them," said Robert Dietrich, of Sun Devil Plumbing.

Sun Devil Plumbing says they see 30 to 40 percent more business the day after Thanksgiving. Potato peels and celery are common culprits, but every now and then, Dietrich sees something that surprises him.

"I think the funniest one is someone put Metamucil down it -- and it turns into a giant gelatin tube," said Dietrich.

“People are afraid to (call on Thanksgiving) because they think they're going to get charged a lot of overtime -- where we don't charge any,” said Dietrich.

If you need a service call at your home this holiday weekend, check rates ahead of time. Some companies charge extra for weekends, evenings and holidays, or tack on a “trip charge” just for going to your home. Others do not.