Why do you have find criteria in your Perform Find step that searches for all records whereTag is empty? That's the result you get when you specify a lone = as the find operator.
If you clear the criteria in this step so that you have:
Perform Find 
You won't find records where Tag is empty.
You also mention a second table (T1) but there is no reference to it anywhwere in this script, assuming Tags is the name of T2.
The other issue that will affect your results is that if you are performing this script from a layout based on T1 (not Tags), You are finding all records in T1, that have at least one related record in T2 that match the specified find criteria. This has been known to create confusion on the part of the developer when, after the find is performed and a found set produced, portals and fields from the related table display data from all related tag records, not just those that satisfied the find criteria.
The other issue that will affect your results is that if you are performing this script from a layout based on T1 (not Tags), You are finding all records in T1, that have at least one related record in T2 that match the specified find criteria
Perfect, that is exactly what I want. I want to show all records in T1 which have a T2 value that satisfy the search.
I don't reference T1 anywhere in the script because I don't want to to anything with T1 except for show the results. I didn't make T2 my active table layout because then my search will give repeat values of T1 in my output.
For example, let's say I have "BREAD" in T1 and "White, Wheat, Rye", as values in T2. If T2 is the layout table and I search for WHITE and RYE, I will see BREAD twice! I only want to see BREAD once.
Am I thinking about this correctly? What information can I provide that would be more helpful?
Your script doesn't use the terms T1 and T2. Am I correct that "Tags" is a table occurrence for T2?
The script, once you have Perform Find, should pull up all records in T1 that have at least one related record in Tags that satisfies the criteria specified in the Tags::Tag field. But since you are in find mode, the data in Tags::tagFInd will not be accessible to specify as criteria unless you have specified global storage for that field. Is it a global field?
When I mentioned that there was no reference to T1, I was making sure that the script is being run from a layout based on T1 as you will get the different results that you describe if you ran it on T2.
BTW, it occurs to me that two Go To Related records steps could be used to pull up the same found set in T1, if a relationship that matches records by the checkbox field were set up.
Also, I find myself questioning whether or not your relationship is set up correctly. I'd consider this relationship for managing such tags:
As I would expect that many records in T1 might all have the same Tag as well as a single record in T1 having many tags--which makes for a many to many relationship here.