Probably the fastest and easiest way to get your building project complete is to hire a plumber (if necessary), get your plumbing issues up to code (permitted, etc.), and ignore the trespass on your property by the state inspector.
However, if you wish to be more aggressive about the trespass issue you can be.
Just because the individual that was trespassing happened to be a state employee, does not give him a right to do so. You can sue both him, and the department, for the trespass. Suing government agencies gets tricky, so whether or not you want to include them probably depends on whether or not you are able to find a law firm that is willing to take your claim (look for law firms that handle what we call "1983" claims (named after 42 USC 1983 - the Federal code section that authorizes civil suits against government employees in certain instances), an attorney or law firm that represents citizens in these types of suits would be ideal).
However, you do not have to name the entity, you can name only the inspector and sue him alone as an individual without worrying about the governmental immunity issues, etc. The fact that you have this individual on camera makes things much easier to prevail (and a law firm very well may be interested).
You can find local attorneys using the State and local Bar Association
directories, or private directories such as www.AVVO.com; www.FindLaw.com; or www.Martindale.com (I personally find www.AVVO.com to be the most user friendly).