That's why one of the most common ways of dealing with tech debt is allocating time for it within other sometimes completely irrelevant stories. For management you can just say "oh I take a bit of extra time for tech debt there", if they're known to take that well, and if not, you don't say anything at all. The ones who you should definitely tell all the details is your team lead / collegues. Like, "oh this is a mess I'll take some time for refactoring/optimizing this next planning", which often implies you allocate this time within other stories.