It is not necessary to "top it off", in my opinion, but you do need to prime a new carto with about 30-40 SLOW drops of liquid. I failed to do that one time (I'm a newb myself) and boy, did THAT taste nastily burned! Couldn't get that taste outta my mouth for hours and never got the burned taste out of the carto, ended up pitching it....

Now, I prime it well, let it sit for about 30 minutes, then carefully start using it. That applies only to a NEW carto, refills shouldn't need priming unless you burned you tank dry. I refill my tank daily, whether it's empty or now, don't want to be away from my liquid bottles and run outta juice. Now, that would be a major disaster, LOL!