Universal third parts of any complete 2-graph and none of DK5

It is shown that there is no digraph F which could decompose the complete digraph on 5 vertices minus any 2-arc remainder into three parts isomorphic to F for each choice of the remainder. On the other hand, for each n ≥ 3 there is a universal third part F of the complete 2-graph 2Kn on n vertices, i.e., for each edge subset R of size [formula] mod 3, there is an F-decomposition of 2Kn−R. Using an exhaustive computer-aided search, we find all, exactly six, mutually nonisomorphic universal third parts of the 5-vertex 2-graph. Nevertheless, none of their orientations is a universal third part of the corresponding complete digraph.