Thats perfect.

I mentioned that an opening at the apex is a possible solution  but
downside was ugly exposed pipe that is prone to heating, but I never
thought to put it *inside* the tank.  Brilliant.

No need for air solenoid if the opening of the Tee is high enough as
gravity will help here, or better yet a one way valve.  Let the Air in
but not the water out.

This also means that i can easily use a submersible pond pump.

Great work.  I knew the list would come thru.

*Inside* the tank, huh just couldnt see the last piece of the puzzle.

Thanks to all.

Cheers Justin

> I like the idea of a pump and a solenoid, but I'd consider arranging
> it differently and use a flow through pump (ie, the pump would allow
> siphoning when not active).
>
> Connect the one tank to the other with the pump in the middle as
> usual.  At the apex of the tube (Which has to be slightly higher than
> the maximum level of either tank) put a T in with the solenoid
> allowing air to enter the tube.
>
> Diagram:
> http://flickr.com/photos/adavis/2590441784/
>
> Note that the solenoid with the air tube can reside inside one of the
> tanks as long as the apex of the main tube is above the maximum of
> both water levels.  This will make it so you don't need to move the
> apex of the tube into the light.  Unsightly tubing could be hidden
> with just one open end of a tube exposed somewhere.
>
> Further, with a more complex control and monitoring scheme, you could
> possibly use the pump to merely prime the siphon, and then when tank 2
> is full enough open the solenoid to stop the flow.  Very low power
> with a low power solenoid.  the solenoid can be very small relative to
> the water flow and still stop the siphon action, and it could even be
> a relatively cheap air solenoid.
>
> If the inner tank is at a higher level then you'd merely use the pump
> continuously.   This requires more information about the levels of the
> tanks relative to each other, though, so it may not be practical
> unless you can arrange them so one is always higher than the other.
>
> The pump can be anywhere along the main line.  Regardless of your
> solution you might consider putting a cheap float valve on the inside
> tank in case the electronic level monitor fails, controls fail, or
> other parts fail.  This would prevent flooding.
>
> If you want to go very cheap, you can take the solenoids you migh find
> that run on 120VAC and re-wind the coil for a lower voltage.  They
> aren't terribly energy efficient, though, so you might still be using
> a lot of power to overcome the friction and spring in the valve.
>
> Also, note that the the typical sprinkler valve has a small solenoid
> you might be able to use without too much modification:
> http://www.spudtech.com/content.asp?id=21
>
> -Adam
>
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