The arson occurred at about 3:50 a.m. in the 2000 block of Broadway, police spokeswoman Sgt. Lyn Tomioka said.
The 20th portable toilet fire happened Jan. 22 in broad daylight in the Marina District. It was reported just after 1 p.m. near the intersection of Marina Boulevard and Scott Street, Tomioka said.
No arrests have been made in the string of lavatory arsons, most of which have occurred in the nearby Russian Hill neighborhood.
