How are vertical stacks connected onto a sewer line?

Vertical stacks are typically connected to a sewer line using a hub that is oriented to receive the vertical stack from above, which is referred to as "hub looking up." This configuration allows the waste and sewage to flow downwards through the stack and into the sewer line efficiently, ensuring proper drainage and minimizing the risk of clogging.

In this arrangement, the stack is inserted into the hub, which is designed to accommodate the vertical pipe while maintaining a secure connection that prevents leaks. The upward orientation of the hub allows gravity to assist in the movement of waste into the collection system, reinforcing the effectiveness of the plumbing design.

In the context provided, the other options do not represent the standard and correct method for connecting vertical stacks to sewer lines. Therefore, understanding the mechanics and design principles behind this specific connection is crucial for effective plumbing and compliance with building codes.