You should read mysteries of the vortex (part 1) and (part 2). It was written by the owner of Silverprint and is a thorough investigation of FB print washing.

Basic conclusion is you need surprisingly little water but you do need movement of water over the paper surface to aid defusion of fixer out of the paper.

HCA and short fix times are your friend.

I use fewer changes of water but regular manual agitation to wash my prints.