Here Vent connections are located at high points and drain connections are located at low points of piping systems based upon the physical piping configuration. The main purpose of hydro static vents are to expel the air present in the pipe while filling the pipe with water for hydro testing. including drain connection with shield ,thermostat , threaded rod , welded anchor, air vent and cluster plug drainage systems are usually out of sight junctions were not always used when two separate drainage runs were connected together, often a hole would be knocked into the side or crown of the outfall pipe and the incoming pipe would then be butted up to this point. for more details of Drain pipe connection download this file .