What is the function of reserving two 50 sewer pipes with an interval of about 40 in the bathroom? B

Sewage, toilet access to the pipe called the domestic drainage riser, the other pipe called the special ventilation riser, the current installation of the drainage riser specification is De110, its drainage capacity is a certain limit, beyond this limit, it is necessary to increase the special ventilation riser, otherwise the drainage will produce air resistance, affect the drainage, and the higher the floor, the greater the impact.

The relevant national regulations on drainage stipulate that the domestic sewage riser of multi-storey buildings or public buildings with high building standards and more than 10 floors (including 10 floors) should be set up with a special exhaust riser, and the connection between the ventilation riser and the drainage riser is called H pipe, which is a pipe fittings specially used to communicate the ventilation pipe and the drainage pipe. Therefore, there will be no drainage in the special ventilation riser, so there is no access port on this pipe, and only the drainage riser will be layered with access openings.