Bottom Drains are essential part of building any successful Koi Pond or water garden. They help remove solid waste and increase water circulation.
As a general rule, solids will sink to the bottom of the pond. The solids can then be removed by flowing into the bottom drain and then removed by your filter system where these solids will be extracted from your pond system.
As a general rule, one bottom drain for the first 5,000 gallons and then one drain for every 3,000 to 5,000 gallons thereafter. Of course, the size of your pond will have a lot to do with this - as will the flow rate you want through your filter system.
Bottom drains - or the pipe work from the drain to the settlement chamber should not be too long. This is because although there is water flow through the pipe work, the heavier solids tend to settle out and can build up in the pipe work itself.