One of the best ways to 'd0' the Koropuku is as a through trip including Townsend Hut in the Taramakau.
Crossing the ridge between Townsend and the Koropuku has no difficulty for the average experienced high-country tramper capable of their own route-finding, and with personal knowledge of weather conditions in this type of country.
The route between Townsend Hut and Big Tops Hut in the Koropuku is marked on the map here in red and is only shown to indicate the general line of travel. It should not be used as a GPSed route.
In good visibility the route between the huts is obvious and your own judgement should be used in selecting the best micro-route around obstacles.
However, if coming down the Koropuku the exit from the stream near to the hut might not be obvious as cairns are often washed away. Keep a lookout for a small overflow stream on the true right of the Koropuku that runs into a quiet watercourse overhung by low trees. It will be obvious once you enter the watercourse. If, instead, you continue in the Koropuku until it begins to drop into a gorge that is a good enough sign you 've gone too far.
Be aware if travelling in the other direction that there is no guiding feature leading down to the Townsend Hut in bad visibility.
Very fit trampers won't find it too onerous to do this in two days in the mid-summer months. For the first time I would recommend taking three days. And my preference is for starting with the first day into the Koropuku.