Sites offering searches for multimedia differ in search options and methods of searching. Most sites will have a section that will teach you how to use their site. Many will have drop drown menus or checkboxes to filter your search. Use them. Look around at each site to find this section and become familiar with their specific search tips. Of course, some search rules and operators are very commonplace, but don't assume that adding a "-" in front of a word does the same thing everywhere that it does at Google.
Some search operators are (almost) universal such as:
Don't use words like "video" and "clip" in your serach. Instead rely on specific words, phrases, or names from the show. On the other hand, other desciptive terms like "screencast" or "comedy" may help to narrow the search.