We study the implementation of fixed priority top trading cycles (FPTTC) rules via simply dominant mechanisms (Pycia and Troyan, 2019) in the context of assignment problems, where agents are to be assigned at most one indivisible object and monetary transfers are not allowed. We consider both models - with and without outside options, and characterize all simply dominant FPTTC rules in both models. We further introduce the notion of simple strategy-proofness to resolve the issue with agents being concerned about having time-inconsistent preferences, and discuss its relation with simple dominance.