As a rule, plan to consume 1t of titium every
2Ly 4Ly your FC goes. I think that this might be affected by how much is in your FC's storage, but I can't confirm that. So if you are planning on going on a 22KLy trip, plan on storing up at least 11000t of Tritium. There's even a tool to help you with these calculations at
https://www.spansh.co.uk/fleet-carrier.
Having just completed a trip from the bubble to Colonia in my FC, I'd recommend carrying at least 2000t above what you plan on needing. This will allow you to do incidental exploration and take deutors while you travel. Lastly, if you need tritium or find tritium overlaps while out in the black, there is the newly-formed
Tritium Pathway Network (TriPN). If you need help validating a potential hostpot, the wonderful folks at the
EliteMiners reddit will be more than happy to help out (and we'd like to know about your finds too).
Hope this all helps!