At some point you may want to do an Enterprise Search query and specify that the results come from a particular content source. A lot of times you might create a custom scope with that content source in it, but if you don't want to create a new scope, you can just query the content source directly. The syntax is simple. Just use it like in the example below.
ContentSource:"Local Office SharePoint Sites"
In this case, I want everything to come from the Local Office SharePoint Sites content source. You can of course combine it with other terms as well like in the example below.
Bike Color:"Red" ContentSource:"BDC AdventureWorks"
In this case, it would search for red bikes in the BDC AdventureWorks content source. Kind of a simple tip today, but I really haven't seen this documented anywhere.