I have been working as a plumber for a long time, more than 15 years. Sewerage installation in apartment buildings is a simple duty of any plumber from the housing office. At the beginning of my career, I became interested in marking on sewer pipes. They usually indicate the material of manufacture of pipes, the date of manufacture and the degrees under which the sockets are located.
Most plumbers with whom they had to work in tandem do not know practically nothing from this marking. What for? Issued and okay. And such a simple question: Why is it that in some sewer tees with a diameter of 110 and 50 of a diameter, an angle is prescribed not at 90 degrees, but at 87.5... drives them into a stupor.
Really strange, all the plumber says something- "Give me a tee for 90°" and not otherwise. Even the store does not bother, but writes as convenient for them. In addition, when they write the amount of material, it always indicates that the tees have an angle of 90 °. Nobody ever writes 87 °. In my memory, this practically did not happen. Now I will tell you this eerie plumbing secret why such an angle is used in sewer tees and crosses:
Such tees, having a non-standard branching of the 87 ° socket, are necessary when installing vertical risers. With correct assembly in a multi-storey building, such a pipe has the necessary, correct angle in advance for pipes that fit into this tee. 2.5-3.0 ° allow you to create a slope for smooth drainage of human waste products, etc. liquids. Accordingly, the installer only needs to maintain this angle when joining the wiring from the apartments.
Sv Plumber - Timofey Mikhailov