Is one allowed to answer Amein between mayim achronim and starting benching?
Answer:
One should not answer Amen after Mayim Achronim, unless they can wash again after the Amen.
Sources:
See Aishel Avraham Siman 179 [in back of Shulchan Aruch], see also Sefer Tehila LDovid to Siman 181