When I drain and fill an SM420 4-speed, I remove the shift lever and pour the new oil down from the top.
For maintenance top-ups, after having tried various pumps and tubing, I now top-up the fluid to the fill level (warm transmission) using a 1-quart plastic gear oil bottle that has a fill spout. I use that bottle at a downward angle, needing no tubing. Or, I can attach short tubing to that 1-quart squeezable bottle.
