Before explaining how to perform this process, it's probably be better if we first talk about why use it in the first place.
As you probably know, there are many reducing agents that will reduce ionic gold into the metal, such as: SMB (Sodium MetaBisulfite), copperas (Iron II Sulfate), Sulfur Dioxide Gas (SO2), Hydroquinone, formaldehyde, hydrazine Sulfate and many more… each has its own applications and pro's / con's.
The washing process is probably the most important one as it will remove the majority of contaminates that ha been dragged out of solution along side the gold. Metal contaminates such as Copper, Nickel, Platinum, Palladium and Silver (Chloride).
Before we start, you should know that there is some dispute regarding a direct Aqua Regia (AR) refining process for high gold content alloys, main reason for that dispute is usually the silver content, which, react with AR and convert to Silver Chloride (AgCl) and somewhat retarding the process. Some refiners just don't like to deal with AgCl and will prefer Inquarting process to eliminate the silver (and base metals + PGM) all together prior to gold dissolution.