How to Setup Chromecast
First or all you will have to setup your router to use our DNS as you can't set the DNS manually on a Chromecast. For this purpose please see our setup guides.
Secondly the Chromecast if programmed to communicate with Google´s own DNS servers: 126.96.36.199, 188.8.131.52. As a result the Chromecast will communicate with the the Google DNS servers even if you have set your router to use Unlocator DNS. So in order to use Chromecast with Unlocator DNS you will need to block access to Google DNS from the router.
Please note that some of the guides mention Roku - this is because the same approach is needed for the Roku as well