How do I know if this will reach my oil?

The hose goes down the dip stick tube and then touches the oil pan. Then it vacuums up the oil. The tank holds 3 quarts which is plenty for small engines.

this is not intended for Car use. It only holds a quart or two of liquid

It would take forever to pump out several quarts of oil. You would have to empty the unit several times. The hose would not be long enough, but you could buy additional hose.