Changing oil in foot of boat motor

[Kent]

They make a simple pump, that attaches directly to a bottle of oil and that is threaded so that one can attach to the bottom hole (while the outboard is vertical) and then pump oil until oil starts to come out the top hole.  Put the plug back in the top hole and then put the plug back into the bottom hole.  Good idea to replace the washers at the same time.  The way you are doing it could result in air bubbles being trapped inside of the lower unit.