If you're a regular BART rider, there is a good chance you've seen a gross thing or two on board, from poop smears to hypodermic needles to what employees call "hot lunches" — their code for vomit.

And if you think BART is dirty now, it was far worse decades ago. Rhonda Morrow started cleaning BART train cars as a temp in the 1980s. She says back then they'd fill up an entire trash bag cleaning just one car, and they never had time to give the cars a detailed cleaning. Just four employees were responsible for getting over 130 cars picked up every night, an average of over 16 cars per hour.

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Today, with upwards of 130 full-time employees working around the clock seven days a week, BART employees do what they can to keep the fleet of 683 cars clean.

Morrow has worked her way up to foreman overseeing the night crews responsible for cleaning train cars when they go out of service for the night at the Millbrae and Daly City stations. Her crews, usually consisting of four people, do a basic sweep of each of the 75 to 80 cars that come through, picking up trash, sweeping up smaller messes and doing a quick mop of the floors. Every night they also detail two of the dirtiest cars, selected by Morrow. To detail the BART cars, they scrub them down from ceiling to floor, spraying disinfectant on the handles and bars, scraping up gum and even steam-cleaning tough spots as time allows. Each car gets detailed every 60 to 90 days.

When Morrow started as a temp, she had two young children. The graveyard shift allowed her to be home to put her kids to bed and back in time to get them up for school. One year she switched to a day shift, but supervisors asked her to go back to nights to help get the Millbrae trains cleaned up. She says the trains on her line have been the cleanest in the BART system since.

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Things have also gotten a little easier since BART implemented mid-line and end-of-line train cleaners that monitor the trains throughout the day, picking up trash and cleaning up fresh "hot lunches" as they see them. This leaves the night crews more time to focus on the trickier and more time-consuming cleaning jobs like gum and graffiti.

Check out the video at the top of this story for a closer look at how BART workers scrub down the dirtiest train cars.

It's a dirty job, but Morrow tries to instill pride in her crews for what they do. She is tough and doesn't tell her crews when she is coming and going between stations to keep them on their toes. But she has relaxed a little over the years.

"I'll ask someone to go back over a spot, but I try to remember that this isn't the White House we're cleaning."

One of the workers at the Millbrae station, Robert Spears, echoed that pride. "My daughter rides these trains. That is why I do it. That is why I clean them."