I think it would be very easy to suck a small amount of oil out with the MitiVac. To avoid contamination you would need to clean the tubes and container out after each use. This could be done by sucking a parts cleaner or other solution through the unit that would dissolve the old oil. Keeping the tubes and unit clean between uses would depend on how and where you store it.
MitiVac must have changed the design because mine has an expanding plug to seal the pouring hole on the top. I agree that the container can be top heavy when full so I just empty mine into a cheap plastic gas can for disposal. Did you ask the company to replace the unit because it cracked?