External hanging type drainage method for space-limited steel hanging box

The invention relates to the technical field of building construction, in particular to an external hanging type drainage method for a space-limited steel hanging box. After entering, water moves along a drainage slope on a bottom sealing concrete face, the water sequentially penetrates through an inner formwork, a supporting square timber and a side plate of a steel hanging box through a connecting pipe to enter a water collecting pipe, and when the accumulated water height in the water collecting pipe enables a floating ball switch to rise to the limit height, the floating ball switch controls a water pump to start to work; by means of the method, the accumulated water on the concrete surface can be automatically drained, the water pump is automatically started to pump and drain water, the whole process of manual watching is not needed, the labor cost is reduced, and the working efficiency is improved. Dry pumping damage of the water pump is avoided; according to the method, the situation that the concrete