A picture is worth a thousand words, so here's some pics, a few design revisions, and some new questions:
(Please ignore all the planters... they're all just temporary plant holders LOL)
I tweaked the hose outline today and re-measured, and this layout is actually 8.5' x 5' x3'. I plugged that back into a pond calculator and came up with just shy of 1000 gallons, and the calculator told me I need a 15x20 liner now rather than a 15x15. So that will be a bit more expense there.
So here's a pictoral layout of the filtration design:
Water will enter The Beast (as I'm now calling the Laguna Skimmer Filter) both through the skimmer opening (the filter will be buried, pond walls built up with dirt about 6" or so over ground level, and I'm anticipating the pond water level to be around where ground level is now) and through a bottom drain.
The bottom drain will probably be placed just to the left of where the big planter is sitting now.
I know a bottom drain technically isn't necessary on a pond this small, but I'm actually considering it another safety measure to make sure to keep water in the filter just in case my pond levels ever drop; evaporation in this part of the world is killer (I have to top off my 90gal tank inside the house about 20 gallons a WEEK this time of year...)
I'm planning on using 1.5' flex tubing to plumb the bottom drain into the front side of the filter, with a ball valve up against the filter to shut off the bottom drain when needed.
**Questions:
1. I'm looking at the 4" Koi Toilet II bottom drain since it's the only one I can find with a grate over the top to help keep small fish out. For some reason, the 4" is the only one I can find with the grate top option; is this the case, or do the smaller versions also come with grates? Or would there be a better BD for me to use rather than the Koi Toilet?
2. Is there any reason not to use 1.5" flex tubing to connect to the bottom drain (with pvc size adapters, obviously...)? Should I use rigid PVC at least part of the way to ensure stablity, or should it be OK as long as I still use a cement collar for the BD and follow Birdman's How To install thread?
3. I'll have to figure out some logistics with keeping the ball valve operational since it will be below ground level. Would I be better off with a knife valve?