Okay, here's my first attempt at a drain design, as I see it. First, I should mention that the pond being fed and filtered by this bog has a raised edge of a little

more than a foot. This bog will have to be raised high enough for the return water to flow over the back edge of the pond. If the foundation I described doesn't raise it high enough, I'll know before I start installing the liner.

First, there will be a "foundation" of those flat, concrete pads, about fourteen inches square. On those will be a "solid" floor of cinder blocks,for height. Then, a perimeter on three sides, of more cinder blocks - stacked two high - to hold the sides of the liner up. The drain would be in a low spot formed by something like sandbags sitting hidden under the liner and arranged to form a shallow funnel shape. At the lowest point, I'll make a hole in the liner and install two of those pvc flanged fittings with the liner sandwiched between, and "marine gooped" and silicone sealed to it so it wouldn't leak. The flanged pipe would connect to a vertical pipe and then an ell, to go out a gap in the back of the cinder block base. We already have a ground drain right there. If I cover the sides of the blocks and just leave the end of the pipe exposed, it won't show much. Plus, it would usually be capped. The small amount of water that would fill the pipe would not matter to the function of the bog. Then,when it was time to clean the bog, I could just uncap the pipe at the back, and run a water hose into the bog to wash the dirty water down and out the back, to the ground drain.

Now, up in the gravel bed itself is buried a shallow plastic kitchen colander that has had the holes enlarged just a little, so that those holes are still smaller than the gravel size. It is upside down over the drain hole, to keep the rocks out of the pipe and drain.

This would be easy to clean, but my understanding of the purpose of a bog is such that you would only do it once or twice a year. If it got very dirty in between times, I could just drain it a little and then cap it back up without actually using a hose. Does my description make sense? Does anyone see any structural or filtering flaw in my design? I really hope I can get this set up for easy maintenance. Please contribute any comments, pro or con.