Sorry. I am quite new to Duolingo and totally new to the discussion boards. I did not now that it's about to vote any replies. I was just trying to be helpful in that I confirmed your "Oder?" question.
Die Regentonne fuellt sich mit Wasser und die Regentonne fuellt sich an. The second part means the barrel is in the process of getting full. The prefix "an" frequently indicates a process not yet completed, like anziehen, anweisen, anordnen, anprobieren.
Germans usually say "anfassen" if they want to touch something/someone. Sich anfühlen is used like you did in the first example.To feel may be used in a sentence like "I feel fine - ich fühle mich gut"