T-Line
A T-Line is a simple alternative to a pressure tank, air-trap or any other filling, bleeding, and draining device. It is constructed by plumbing a "Tee" connector (tri-barbed, with a perpendicular secondary flow-pattern, shaped like the letter "T") into an existing tube thus creating an alternate flow-path. However, instead of routing the secondary path back into the system flow, it is simply left open or closed off using an end-barb or other capping device. The tube itself thus can act as a mini-reservoir and allows air-bubbles to travel into it as they are caught into the "Tee" connector, and ultimately travel out of the system (bleeding).
A common use for a T-Line is in a watercooling system such as those found in enthusiast PCs. The T-Line is an integral part of a do-it-yourself watercooling system alongside the traditional choice of a reservoir. Major reasons for choosing a T-Line over a standard reservoir are cost, simplicity, and space constraints.
"Fill-Ports" (example "The fillport" by DangerDen) are specifically made with T-Lines in mind, and serve the purpose of capping the T-line in an air-tight and re-openable/re-sealable fashion. They are available anodized in various colors and thus able to be tied in with color-schemes.