From Manson Biv head out to the open tops & follow the ground trail 200m NE to pt. 1257. Make sure to locate the orange triangle on the bush edge so as to pick up the marked DOC track that drops in a NW direction into the bush saddle. The climb out of the saddle is short but steep, bringing you to bush edge, where you skirt around the end of the bush & climb very steeply to an un-named highpoint. Once back on the open tops, skirt the south face of the first peak to pick up the obvious clear spur heading due south. Follow this to where it starts to drop steeply (still on open tops) towards the main creek. At around the 1200m contour, look out for a vague spur dropping SW with a tongue of beech rising up it to nearly meet the main spur you are on. Take this side-spur SW & drop with it to the river. The top of the spur becomes scrubby but the going just south of the crest is good in open (though steep) beech forest.
On reaching the Tapahiwhenua Stream, head 80-100m upstream, ignoring the first small sidecreek (not shown on maps) to the sidecreek draining from Old Manson Hut. Follow either the creek or the spur to its north uphill (west) until a large grassy basin opens out beside the creek. Old Manson Hut sits at the back of this basin. A vague old flagging-tape route runs from Tapahiwhenua Stream to the hut but it is ill-defined.
Note: Described in the reverse direction to your journey
When standing in front of the Old Mansion Hut looking downhill towards the lower end of the grassy basin, head to the lower right hand corner & follow vague, ill-defined & old flagging tape down the small un-named side creek to the Tapahiwhenua Stream. Head down Tapahiwhenua Stream for 80-100m & climb up on to the true left bank to the base of a rugged-looking, & scrubby but open side spur. Climb in a NE direction, picking your way through scrub near the bush edge on the crest of the spur. As you gain height the scrub lessens & the going becomes easier, eventually reaching the bush edge & open tussock tops where you can look back into the bush-basin holding Old Manson Hut. Once on the open tops the spur becomes more defined & it sidles to the south of an un-named high point (SE of pt. 1412) eventually meeting the DOC poled route that runs in a NW-SE direction from Mansion Biv.
Upon meeting the poled route stick to the spur as it descends steeply to the bush edge, which it skirts around the bush for a few hundred metres before an orange triangle indicates where to enter the bush. At this point the route becomes a track & the decent continues through the bush to a saddle NW of pt. 1257. The climb out of the saddle is straightforward & the track soon emerges back out on to the open tops where a ground trail climbs & skirts along the bush edge towards pt. 1257. The trail swings SW for 200m to Mansion Biv, which sits just inside the bush edge. Note: do not swing into the open country after emerging from the bush saddle, stick to the bush edge ground trail.