take the s-bahn/u-bahn/tram to Moosach and catch bus 176 to Rangierbahnhof, or s-bahn to Fasanerie and then bus 175 Ludwigsfeld Campingplatz (end stop). These bus stops are either side of the Dachauerstrasse bridge that goes over the goods depot (and close to the hump).
Buses run every 20 mins, as do s-bahn (S1). u-bahn (U3) runs every 10 mins as does tram 20.
You'll need an innenraum day ticket which costs €5,40
I'll sedn you a link to an aerial view of the site (the website doesn't like links being posted on other sites)