I had one many years ago and I if I remember, to start the siphon you hold the unit upside down, below the water level and turn on the motor. Once the siphon start flowing thru the filter, you turn the unit right side up.
yes you start the filter upside down, then slowly turn too side, you may need too hold it on it's side for a bit for it too fill. i run mine once in awhile, and starting them is a pain, but well worth it, for how it cleans.
I just suck on the other end to get the syphon going and this usually gets it going, but sometimes its tricky, an awsome piece of equipment, but a paint to clean and start