David has an article about creating a “holding tank”. It offers a subscription to a list. But when I try and subscribe it states I don’t have permission. Is this no longer available? Holding Tank Default Policy
I believe this has to be given to you via the Support team
The subscription talked about in the article is no longer directly available. But it’s easy to find the domains by searching the web for what the connectivity check URL is for each OS. For eg. Windows uses www.msftncsi.com Android uses www.gstatic.com and iOS captive.apple.com
There may be more, you can always check your domain log via MyTools to see what the first lookup attempts are from devices you connect to the network.