Wouldn’t your IT department be able to see an attempt to access this site regardless of whether or not it’s classified as adult? And wouldn’t an adult label make it more obvious that you’re attempting to access something you shouldn’t using civil service resources?
Just be more careful about what sites you visit while connected to civil service networks. As a rule, I don’t connect my personal devices to my employer’s network except where absolutely necessary, and I don’t use my employer provided devices for anything unrelated to work.