Not that this bit of advice will ever be helpful or comforting… When using a powder, pour it into an empty glass. Add the minimal amount of hot water needed to saturate the powder. Mix the powder as thoroughly as possible, then slowly add the liquid you intend to use for palatability, mixing constantly. This will provide you with the least clumping and most dissolution, making the drinking of it less objectionable.
Thank you for honoring your father’s wishes and being his reluctant witness. He needed that small talk, and you needed those last moments, even if you don’t remember the content of them.