The utility model relates to a bowknot for intermittent type formula vacuum pre -pressing drainage that breathes freely, the main part is a flat cube of both ends open -ended, be connected with last drain bar and lower drain bar respectively, both sides all are provided with airtight cavity passageway (11), the bowknot is provided with port (5) of running through the bowknot of connecting transverse drainage pipeline (1), set up the mouth (20) with the inside intercommunication of bowknot inside the bowknot, top and below running through the port of bowknot (5) respectively are provided with two vent pipe port (6) that link to each other with vent pipe (3), the position that is close to upper end and lower extreme in the both sides of flat cube respectively is fixed with a cavity and ventilates connecting pipe (7), and the one end that connecting pipe (7) were ventilated to every cavity all is linked together with corresponding vent pipe port (6), and the other end and airtight cavity pipeline (11) are linked together. The utility model discloses can make the contribution for drainage pipe network and vent pipe network alone operation.