The installation of a bottom drain for a Pond is solely for the benefit of the Pond owner, it is definitely NOT beneficial to any resident fish.
Although I don't use bottom drains on any of my installs, I do have a few Ponds that I service that have bottom drains. I probably get problem calls twice as often on those with the drains as opposed to those that don't.
For a bottom drain to work properly you can not rely on gravity. The water must be lifted to either a settlement chamber or directly to the filter. An external drive pump is required for this (some of the newer submersible Mag Drive pumps may work). Using an external pump on your Pond would probably be overkill. Based on your indicated Pond size, you have a capacity of less than 1000 gal., probably closer to 750. The smallest external direct drive pump available is rated in the neighborhood of 2200 gph, which would circulate your pond volume about 3 time an hour. This will create a quite powerful suction at the aperture of the bottom drain possibly posing a danger to any small fish and would greatly ****** the invertebrate population growth which is necessary for a healthy Food Web.
The addition of a bottom drain will also preclude the use of a gravel bottom, which is also quite important for biological balance.
I find it interesting that you were referred to koiphen.com (which IS an excellent site) in regards to the benefits of bottom drains. One of the main threads on this particular site is 'Mud Ponds' which ,of course , are perfectly natural and, for sure, do not have bottom drains.
Will this be a bare liner Pond? Will you rock the interior walls? Will you include planting shelves?
I would forget the bottom drain idea. It is going to be difficult enough to achieve any semblance of biological balance in a Pond of this capacity without adding an unnatural device that will add to the initial expense but may or may not save you maintenance time.