The Filter Track runs from the Scenic Drive for just under a kilometre down to the service road a little west of the Filter Station, or vv.
I’m not recommending this track if you’re in a hurry. After a gentle enough start, it descends very steeply, and one is frequently lowering oneself to the next step below by hanging on to tree roots at eye level. However, I’m 68, 180cm, and 140 kg (blushes) at present, and I can tell you it’s manageable both ways, if you take your time and go carefully. ARC time 45 minutes. Fatman time, 68 minutes each way. In wet weather or after recent rain, I wouldn’t bother.
A full report and photos at http://wudhi.com/mrwalker/filter/filter%2001.htm.