Slide 5 of 24

Drains: One element where flow enters the system in an ISBL unit. Liquid falls from a point of discharge to the level of flow in the underlying sewer. Drains may be sealed or unsealed. At unsealed drains, both liquid and air can enter the sewer system. Sealed drains have some type of trap (e.g. P-trap) to prevent air from entering the system.

Hardpipe connections: Another element where flow enters the system in an ISBL units. Unlike drains, flow enters the sewer at the level of existing flow.

Junctions: A point at which any two or more pipes meet.

Drops: Drops occur at junctions where the inflow branch or branches are at a higher elevation than the outflowing branch. The liquid must then fall some distance before flowing further.

Manholes: Manholes are points of access to the sewer system for maintenance reasons. They have small openings (pickholes) so that the manhole covers can be removed. Air can enter or leave the system through the pickholes.

Reaches: Reaches are the pipes in the sewer network. A new reach exists wherever a manhole, drain, drop, or change in direction occurs.