I think as long as you clean it properly (actually seriously work on it) and convince the airport staff that you're aware of the issues and you've cleaned it properly, it's likely to be okay.
I passed through Hobart yesterday, which has a big sign in the departure terminal warning about Didimo, and specifically targeting everyone heading to NZ and back. Until seeing that, my experience with Aussie airports (notably Melbourne) has seemed fairly relaxed compared with NZ. I guess Tasmania's especially concerned about that kind of bio-security, though.
I've been through NZ customs many times with a tent and as izogi quite rightly says, as long as its clean and you've made an effort, though they will still check it, as they should too, they don't usually give you any problems.
The same goes with all tramping gear, boots, poles etc.
I agree that here in Oz we tend to be more laid back but we still do the checks when necessary....at least that's my experience.
Personally I have no issue with these bio security checks, as I don't have a problem with other airport security checks, I'm just glad there's people looking out for the long term security of both our countries.
Zaire and much of Africa has endemic Foot and Mouth disease. The strain over there is relatively harmless (to there cattle at least) but the powers that be dont differentiate between that and the strain that saw half the livestock in Northern England slaughtered a few years ago. Any form of foot and mouth will cripple our farm industry for a long time. Better safe than sorry.
Re didymo its amazing how quick it spread through the south island but never got to the north. I wonder how long it was there before anyone noticed
My husband and I waited and waited for our tent to be inspected at Auckland airport on our way back from Alaska. Finally I went up to the closed lacth down door and knocked on it. "Is our tent ready yet" I asked after having waited patiently for seemingly an eternity. "Here it is" they said..."it's been ready for ages." Obviously if you don't ask them they are not going to sing out to you.
