And I respect your right to disagree. Lively discussion is always eventually leads to what is true.
Even though they are called 'Gravity Fed', the water is not going to move through the drain without a pump creating the flow. I just don't believe that the terminology is accurate, even though it is accepted in the Pond industry.
I want to make it clear that bottom drains DO WORK, and quite well. What I have a problem with is that the use of a bottom drain indicates a bare liner Pond which is a completely unnatural aquatic environment. There is no way to approximate a functional aquatic eco-system in a bare liner Pond.
The primary purpose of a gravel bottom is not to provide bio-filtration, but to provide habitat for a wide diversity of invertebrates that are crucial in the reduction of organic waste and debris to simpler forms that are subsequently used as food by other invertebrates. These same invertebrates form the base or foundation of the aquatic Food Web. Without a nominal invertebrate population, the aquatic environment will never be in balance.
A 'Gravity Fed' bottom drain system requires that all of the modules (settling chamber and filtration chambers) be located below the Pond's water line. This requires excavation of an area large enough to house the modules and provide access. In Bbentler's case, this required area, to me, is not justified for a 60 sq/ft Pond. A Skimmer and an adequately sized bio-filter will ensure that the basics for water quality are provided.