Hi, Matt,
One possible cause may be overfilling your expansion bottle/radiator. If you fill it to the top, when it heats up and 'expands', then it will overflow and the syphonic action will cause virtually all the water to leak out. There should be a level marker in the bottle or radiator...fill it to this level only. Don't be tempted to fill it to the top. It needs room to expand as it heats up. Also, only fill it when the engine's cold....if you fill it when it's hot, you'll again put too much water in it as the level will be higher where the water's hot. Give this a try. Best of luck!!
Denis Langley (Car Aid Mobile Mechanic)
September 2008