We spent 6 weeks doing the northland coast a couple of years ago. At Opua and Marsden Cove marina we were asked for the following Proof of insurance, proof of when the hull was last cleaned and holding tank.We carry copies of the insurance certificate and the last haulout which they take copies of.At Opua they provide a big cable tie to go around your holding tank dump valve and they sometimes come aboard and check that you are using it.At Whangaroa the harbour master was going round the boats and asking about holding tanks they did not board and I believe you can refuse them board though I mi