Some people like to use a syringe on the screw hole, me, I top fill. Pop the drip tip off, loosen screw slightly, slide carto down until the top of it is below the top seal. Hold the tank at a slight angle, tissue on the bottom of the carto, pour liquid in at the top. Slide the carto back up, reattach drip tip, tighten screw. Blow through the drip tip to remove any excess eliquid in the carto, and wipe the connector.
I top off once a day at work, once early evening, then just before I go to sleep. Carrying even a needle-less syringe just to refill isn't for me, I use a little 6ml dropper bottle of eliquid. Total time to top off is about a minute, from unscrewing the tank to putting it back on. Orings are still good, I've been using the same tank since they first came out, no problem replacing the rings whenever they do go bad, they've given me good service.