A drainage system allows excess water to drain from a pond, and they are of varying complexity. The end that is in the pond would be called the "intake" or "inlet". Water flows into that end. The opposite end is called the "discharge". Water flows out of the discharge. If you go to "Questions and Observations" and scroll down to "Overflow Pipe", You'll find a discussion of a simple system. If you need more information, Call Nicole at the Pond Boss office and I feel sure that she would suggest a book or books that explain drainage systems in great detail.