I'm gonna' weigh in with a hillbilly method.....we used to drain the HBG pond every year, using rigid, 4" pvc pipe. Our setup sounds very similar to what cold is describing, with the exception that we didn't glue all the joints. We needed to be able to disassemble the contraption and store it, between uses. That's hard to do with a 70' piece of pipe.

The joints that we didn't glue, we simply wrapped tightly with Saran wrap. Don't laugh, it worked for years.

We ran a 3' piece of 2" pipe off of a T, placed where the vertical section coming out of the pond met the horizontal section going across the dam. The 2" pipe contained a valve, was capped on the end, and a barbed hose fitting of about 1/4" or so was threaded into the cap. To start the siphon we used an engine cleaning wand....the kind that attaches to compressed air and has a suction hose to apply detergent. We used a gasoline powered air comp. to provide the pressure.

To cap off the pipe on the downhill side, we jammed in 2 liter soda bottles. As I recall, they were a near perfect fit. We did wrap that joint in Saran wrap also however. A quick cut with a pocket knife and that bottle would come flying out once the pipe was filled.

To start the siphon, we hooked the wand's detergent hose to the barbed fitting, connected the air comp. to the wand, fired up the comp, and just squeezed the trigger on the gun. When water sprayed out of the wand's tip, the pipe was full. Close the valve, uncork the bottom, and away it went. It took longer to tell about it than it did to do it. We actually loaned this setup out to a couple of other folks who wanted to drain their ponds down.

By the way...trying to feed rigid lengths of 4" pvc out into deeper water can be difficult, as the pipe tries to sink to the bottom and gets very heavy. Capping that end with a soda bottle will make the job much easier, provided someone is willing to go out there and remove the bottle and allow the pipe to sink, once in position.

"Forget pounds and ounces, I'm figuring displacement!"

If we accept that: MBG(+)FGSF(=)HBG(F1)
And we surmise that: BG(>)HBG(F1) while GSF(<)HBG(F1)
Would it hold true that: HBG(F1)(+)AM500(x)q.d.(=)1.5lbGRWT?
PB answer: It depends.