What is a fill?
Adjustments, otherwise known as "fills", are often carried out in the office under local anesthesia. If the port can not be felt you may have to have the adjustment done at the hospital using X-ray to find it. A fine needle is passed through the skin into the access port to add or subtract saline from the band. This process often takes only a few minutes and most patients say it is nearly painless.
This was taken from a website. The port is the access point that is under your skin, normally on the side of your stomach. Think of the band as a small tire with an innertube. The "inntertube" is on the inside of the tire. The injection of saline alters the tightness of the "innertube".
Hope this helps!
Michele