Steel tube core-pulling method, rubber tube core-pulling method and embedded bellows method. Steel tube core-pulling method: before pouring concrete, the steel tube is buried in the formwork, and after the concrete is solidified, the steel tube is pulled out to form a channel. This method is suitable for forming straight pipes, but it is difficult to form bent pipes.
Rubber tube core-pulling method: before pouring concrete, the rubber tube is buried in the formwork, and after the concrete is solidified, the rubber tube is pulled out to form pores. This method is suitable for the forming of straight pipes and bent pipes, and the rubber hose is easy to be damaged and needs to be replaced frequently.