t wash is a solution of acid and thinners that turns the galvanised layer black. Too much and you get a sooty black layer not enough and the surface still remains smooth. The idea is to etch the layer to give a profile to allow the paint to adhere to it, once done you cannot apply an alkyd paint as this reacts with the zinc and peels off you must apply an epoxy or acrylic system.
This solution appears not to be available in australia but I work of a company that produces a material that will adhere very well to degreased galvanised steel.
