x1=k1 is a bathroom, in which x2=l1 washes x3=l2 (self/other(s)/body part), in home/building/structure x4=k2 surrounded by partitions/walls/ceiling/floor x5=k3 (mass/jo'u)
A room with a sink technically qualifies, but this is more like a room with a bath or shower as well. What most Americans call a "bathroom". For a room specifically for urination or defecation, see vimku'a.