FYI, I just came back from the Honda part department. I asked for the 2019 Ridgeline's fluid DPSF-II, and learned that it is sold in one gallon. This triggered my second question is I still have one gallon of the VTM-4 fluid at home for Honda Pilot, is it equivalent to the Ridgeline DPSF-II? The answer was yes; then you don't need to buy another gallon of DPSF-II fluid. So I end up only purchased the two drain plug washers. (94109-20000 & 90471-PX4-000)
Hope this helps.