They wont flow untill septemberish. You need the dams further up to fill first. Just take your cons to the start of slatey, creswick end, and use the dam in old hyd' sluicing area to bank out of. Theres another couple on wolfes road.
You'l want a 4wd to get right up to cottys or it'll be a few hundred metre walk, so carry light. A 5hp pump will suck ass.
Head up into the pines to some the benched areas, plenty of 4wd depressions filled with water u can recirculate out of.
I live 5 mins from cottys, in a month or so i'll be out there quite often, either after work or weekends, hit me up around then an i'll come for a dig mate.
cheers.