Is Al naarot bavel said after mayim achoronim, or before?
Al naarot bavel and Shir Hamaalos are said before washing mayim achronim. The reason is because we should preferably not have any separating (hefsek) between mayim achronim and bentching.
Aruch Hashulchan 181-9, Ketzos Hashulchan 43-1. According to some Rishonim ( Mordechai Brachos 204, Tosefta Brachos 5-14) what he gemora says “Tikef l’nitila bracha” means that washing mayim achronim has to be immediately before bentching. Maharshal 34, Taz O:CH 166-2.