Hello @James Bissett ,
In order for the AKS POD container to communicate to a PAAS SQL Service , it needs a VNET service endpoint followed by a vnet-rule which needs to be added .
I just tried below git hub document successfully , which talks about an AKS POD communication to MySQL PAAS Service.
https://github.com/yoshioterada/k8s-Azure-Container-Service-AKS--on-Azure/blob/master/Kubernetes-Workshop9.md
Able to login to the pod container and perform mysql operations.
Kindly let me know if you have additional questions.