Before installing your Fumoto valve, one of the most important things to check is that your valve lever is in the closed position before adding new oil.
Here's what closed valves look like based on their lever position:
Do not add new oil if your respective valve levers are in the following positions. Your oil will quickly end up on the ground and you'll either be sad or mad. Don't be sad or mad. Instead, ensure your valve levers are not in these positions before refilling your oil: