Bottom Drain Installation At the lowest point of the pond, stub up a 3 inch bottom drain and cap it off. Pre assemble both the 3 inch bulkhead flange, as well as the 1 1/2 flange by screwing the top flanges onto their bases. When cementing both bulkheads on to the pipes, align screw in a straight line. Add cement to hole around drain. Click to see full answer. Similarly one may ask, do I need a bottom drain in my pond?Quick and easy answer, you don’t need one. Bottom drains aren’t necessary under certain conditions, so they can be a waste of money. It’s important to know whether or not you need one because it can make a big difference in the health and look of your pond.Secondly, how do you build a koi pond with a bottom drain? Locate the center of the bottom of the koi pond. Measure end to end and side to side to find the center. a hole large enough for the bottom drain at the center of the pond. Then trench wide enough and deep enough for the 4″ drain pipe. In this manner, how does a bottom drain work in a pond? A bottom drain is used on a pond which has a gravity fed filter system. Water and pond waste leave the pond via the bottom drain, travel along a length of pipe, and into the pond’s filter. Bottom drain set ups are a much more efficient than having a pump situated in the pond, pushing water to a filter.How do you drain a pond?To start emptying a pond using a submersible pump you just need to position the out-take hose into your garden or the area you want water drained. You would then need to place the submersible pump at the deepest point of the pond to ensure you can drain the maximum amount of water in one sitting.