64 (Canadian) Valiant Signet (aka Dart GT) front disc brake conversion

Finalized the block connections and vacuum line hook-up. went through all of the fittings to verify good connections. Should be able to bleed the system tonight or tomorrow. Anyone have an idea on how to best flush out the old brake fluid from my hydraulic bleeding system? Old DOT3 in there and I'm running DOT 5 in this new setup.