What do you do by Duchaning when there is no Levi or Bechor to wash the Kohain's hands?
I believe the Cohen washes his own. If I recall correctly, the Gemara just talks about how Cohanim wash. Having someone else do it is the Zohar.
If there is no levi, a bechor (firstborn) should do so. If there aren’t any bechorim, then the kohein should wash his own hands (M.B. 128 sk. 22).