Green’s Dictionary of Slang

1. (orig. US) a visit to the lavatory; a stop on a car journey, usu. for passengers to relieve themselves or freshen up; usu. as make a pit stop.

1967–8		Baker et al. CUSS 173: Pit stop, take a Urinate. Defecate.
1981		M. Baker Nam (1982) 162: It got to be time that I had to make a pit stop, so I was running around for a place to go to the bathroom.
1992		D. Burke Street Talk 2 172: I’ll be right back. I have to go make a pit stop.
2004		C. Hiaasen Skinny Dip 188: Tool made another pit stop before they hit the turnpike.
2011		J.J. Connolly Viva La Madness 49: Morty reappears [...] all spruced up after his pit stop.

2. a stop on a journey or a rest from an activity to have a drink or food.

1989		S. Armitage ‘Team Lada’ in Zoom 71: Racing home to burnt suppers; late, but with / a bouquet of excuses, keeping mum / about pit stops at the Coach and Horses.
2009		P. Temple Truth 225: Pitstop at Vic’s. Raisin muffin.