Manakau is one of three hamlets (you can't really call them towns, or even villages) along State Highway 1 between Levin and Paraparaumu (the others are Ohau and Te Horo.) Recently (in 2015) the speed limit through Manakau was reduced from 100 kph to 80 kph, so at least if you blink when driving through now, you won't miss it!
Manakau is home to a school, a pub, some small retail and horticultural businesses, and that's about it.
This cache is located beneath what is officially called Bridge 38A, and I suggest to get to it, it is preferable to drive through the underpass and park on Honi Taipua Street, rather than on SH1 itself.
The cache is an Eclipse mint tin.