Episode tags literally do not work. They do nothing! They have not been implemented.
Back when I was posting on Tapas, I just used mine like title text, a little bonus comment on the page, and I'd put character names in there as a reminder of how to spell everyone's names and in the hopes that one day they would do something, but in the entirety of my 2 years on Tapas, the episode tags were never implemented.
Series tags DO work, but I don't find them terrible useful. If you do a search on Tapas for something, then the first results are series that have that word in their title, and the following results are for series that have that word in their series tags somewhere (this search does not search episode tags).
But I've looked into this a few times and I can't figure out what determines the order that series show up in the search results. Like, it's not most recent update, it's not number of episdoes, it's not which series was created first, it's not popularity.... and the order never changes, so if you're far down on the list, and as far as I could find? there's no way to improve your listing.
So if you have dragons in your comic, and tag the series "dragon," then yeah, it'll be in the list that pops up in a search for "dragon," but it might be on page 41, and there's no way that I could find to change that.