Mrs Chalecki said the kittens were in such a bad state, they were nearly dead - "really flat and lifeless for four-week old kittens".
"I don't know if they tried to drown them in the toilet first and then put them in there but I didn't understand how the bits of faeces got in there, I have no idea. So basically just got them out of there and had to wash them and gave mum a bath first and then towelled her off and put her under a heat lamp and then washed the babies which were kind of half dead, freezing cold. They were just really flat and lifeless for four-week old kittens and just really cold. Once things that young get that cold they start going downhill pretty quickly."
All but one of the kittens perked up, so she took it home and nursed it for another 24 hours.
Waikato SPCA executive officer Sara Elliott-Warren was also disgusted by the person's actions and was the first time she had heard of animals being treated in such a way.
"Obviously anyone dumping animals anywhere is reprehensible and also against the law, to dump them in a sanitary bin is what I would class as pretty inhumane and disgusting ... We hear about these bizarre stories from all over the country and this is not one that I have heard of before so for someone to intentionally do that sounds like a fairly unwell mind."
Mrs Elliott-Warren said the organisation needed evidence of a person treating the animal inhumanely before they could charge anybody.
SPCA inspectors would now liaise with police to see if they were successful in obtaining any CCTV footage of the incident.
Asked whether there had been an increase in animal dumpings, Mrs Elliott-Warren didn't believe there was and said it was more likely due to increased awareness from social media.
"I think we've always had quite a lot. Absolutely, I think the stray cat population is growing and that's causing more stress and possibly more numbers of kittens being dumped. Puppies, we seem to be having an influx of them being dumped. I don't think there's more than normal though I just think with social media we become more aware of it."