This is a special type of tube common in most drip systems. They tend to be laid on the ground surface between plants. Emitters are generally installed to these tubes. Drip tubes tend to be made of thin-walled polyethylene and consequently have a much lower pressure rating than other parts of the system. It is generally recommended that these stay above ground as they can commonly be nibbled on by pesky local rodents! In large commercial setups, these tubes are usually “hard-piped” in these systems and the emitters are installed directly onto the laterals.