The theft occurred sometime between February 28 and Friday morning. Only the platform and gates, which are cemented in, are left.
Stella Schmid, of Papatūānuku Earth Mother Tours, said the Department of Conservation had initially supplied her with spray bottles and disinfectant but that didn't protect the trees when other groups visited the forest.
Schmid said she ''had a haka'' until DoC agreed to install the hygiene station about a year ago.
The theft made her feel sad, she said.
''The whole point of the station is to protect our taonga that's going to become extinct if we don't look after it.''
Kauri forests once covered 250,000ha of Aotearoa. Now just 1 per cent remained and that was under threat from kauri dieback.
''They just haven't thought about the consequences of their actions. If people come here from another forest and they can't clean their shoes it could mean the death of these trees. I don't know how they can be so thoughtless.''
DoC Bay of Islands senior ranger Marty Akroyd said the theft was ''annoying, costly and puts kauri at risk''.
''We'll have to fix it as soon as possible. We may have to put in bottles and brushes until it's replaced.''
DoC would consider how to make thefts more difficult in future, he said.
Drench guns had previously been stolen from Forest Pools hygiene station near Ōkaihau but this was the first time a tank had been taken.
The track had, however, been upgraded with metal and boardwalks, so as long as walkers stuck to the track they were unlikely to spread the disease.
The theft was reported to Kerikeri police on Friday.
• If you have any information about the theft call police on 105 or Crimestoppers, anonymously, on 0800 555 111.