Initial setup: There needs to be 1 player in the breakside dump spot at each end. Second person in the stack comes up as marker, putting a one way force on (same force, i.e. flick/backhand, at both ends).
Dump player initiates upline cut.
Dump player continues their cut and receives the pass. Front of the other stack (previous thrower) makes a fill cut, with appropriate timing.
Fill cutter continues their cut and goes to the dump spot at the other end. Player who just caught the disc clears through and joins the other stack. New marker & thrower at the other end. This is one rep complete; we now repeat from the other end.
Dump initiates
Dump receives pass as fill cutter comes through
Dump clears through, fill cutter continues to dump position, new thrower/marker get set.
Two reps complete. Note that you will always rejoin the same stack in this drill.