This is my extension to the GTM Tips post by the excellent Simo Ahava (his post: Remove PII From Google Analytics Hits).

Essentially, I had been looking for a way to block Personally Identifiable Information (PII) hits at the collection level i.e. using GTM, before the hit is sent to Google Analytics. Why do this? Putting the obvious requirement to not gather PII to one side, if you are adding filters to your GA Views in order to delete PII it is too late – the problem has already occurred....