As you enter, you get to a standard box culvert tunnel where about 10m in, the floor and roof drops lower. About 150m in, there is a ramp down to a RCP that continues for the last like 800m of the drain. The drain exits out at a park.
1. The section where roof and floor lowers
Tea Tree drain in Adelaide by Abandoned Sydney, on Flickr2. The ramp to the RCP
Tea Tree drain in Adelaide by Abandoned Sydney, on Flickr3. Looking back from the RCP
Tea Tree drain in Adelaide by Abandoned Sydney, on Flickr4. Pipe continues down
Tea Tree drain in Adelaide by Abandoned Sydney, on FlickrI did reach the exit but I didn't go through as not to be seen by other people but there wasn't really worth taking photos of the exit. Overall I would give it a 7/10.
butbits been 20 years since I have been through.