I have been there. I went out of the University Road in downtown Shantou, walked straight through Shantou University, passed the traffic police examination room, and when I arrived at the toll booth, I could see a sign on the roadside that read "Tropic of Cancer Sign Tower". Turn right and go in. The road inside can't be described in detail, but it's not too difficult to walk. I remember it was at the foot of the mountain about 1 km, and you can see the Tropic of Cancer sign tower on the left. Go along this road. I'm sure you'll see a lot of garbage trucks coming in and out.
You can see it on Google satellite map.