Use tray rinses in a little fresh water to dilute any carry over fixer right down - you only want to wash out the emulsion and base. After that it is wash aid and soaking with periodic flushing of the washer. My wash tank drain goes to the ornamental side of the garden where it will do some good - the fixer residue is minimal. The tray rinses are treated as fixer for disposal.
By removing as much excess fixer as I can, I can wait until I have a full tank for washing. I am thinking of making a smaller set of dividers for my Versalab so I can put in a displacement box to reduce the volume for small batches.