There are two types of drainage systems at your Northern Beaches property one is a stormwater system and one is a sewer drainage system, they are 2 very different systems.
The stormwater system collects all the run off from your roof, it then flows down the downpipes installed on the side of your property, these lines either then go into stormwater pits, tanks, main lines & then eventually end up in the street kurb and gutter.
The sewer system collects all the discharges from a toilet, kitchen sink, basin, shower & floor drain. These deposits then all connect into a main sewer line on your property before finally connecting into the sewer main.