It's A Wash is a car wash owned by Greg, Steven's father. This is presumably where Greg lives in his van as it is almost always seen there. How and when he acquired it has of yet not been revealed.
It's A Wash makes regular, but brief appearances in the show, much like Big Donut:
It is seen again when Steven is taking a full cat form. They decide to rinse the cats off using the wash.
The car wash makes an appearance as Steven is going to look for his father in order to rehearse for Beach-A-Palooza. Due to Steven's distraction, as well as a miscommunication between Greg and Yellowtail, it is partially demolished and set ablaze.
The episode begins at the car wash. Greg and Steven are eating watermelons and the seeds began growing into Watermelon Stevens the next day.
The car wash is featured as Steven and Connie trick Greg into dressing up to spend more time together. The time lapse showing his different outfits is long enough for them to build a snowman.
Greg offers guitar lessons and has Steven hand out flyers. At the car wash, he sits with his guitar ready to teach any newcomers.