Hi. I'm a bit at the end of my rope here. Pond is pretty much dug
and has been sitting naked for almost 2 weeks.

We understand the benefits of a bottom drain & will put one in. But
which one? There are a few different types. Above liner or below?

Someone told me that a standard under liner drain fitting allows a
1/4" gap for the water to flow into. To me... I envision this
getting clogged every day with me constantly fussing with it. I can't
fathom how a lousy 1/4" gap is going to do much gunk removal. I
wanted to confirm this so I called a pond supply company.

Basic Tetra drain - The guy told me that the basic Tetra drain's gap
width would depend on the install. If I want a higher gap - don't
sink the drain so low, etc. He said it could give me a 1/2" gap. OK.

There is a retrofit that looks very nice. Comes in 2 sizes. Allows
for 2,3, or 4" tubing. The bottom of the unit is a big 10" diameter
hole. I was told it rests 5/8" off the ground. I like the idea of
being able to move it around or pull it up if it clogs, attaching the
tubing to something else, etc.

Another drain is W. Limm. I haven't yet inquired about the specs on
this.

My choices a

Tetra underliner drain (pretty basic) with a potential 1/2" gap. Or
1/4" depending on who the heck you talk to.
Lim drain
Aqua Wizard Retrofit (5/8" gap).

Here are pictures: http://www.fancykoioutlet.com/supply/skimmer_drain.htm

Can anyone advise which one to get? I'm stunned that these things
don't allow for a ratcheting up or down to allow more or less water
through depending on your mood/need at a given time. Looks like one
is locked into the gap width with these except the Aqua wizard
retrofit which could be raised up.

I was told the retrofit would be equally effected to an underliner and
if one is in the building stage like I am - the decision would really
boil down to aesthetics. Would this be a correct statement?

Also, the regular tetra underliner has a 3" outlet - can I stick to a
3" PVC? I'd love to because those stupid gate valves are pricey and
the 4" is crazy. The run wouldn't be far. I'd say no more than 12
feet. Can I get away with a 3" pipe?

Thanks