But the bottom side of the siphon doesn't have to be the bottom of the system. Run the tube up 1m to the window and back down out the window perhaps 3m to a buc

But the bottom side of the siphon doesn't have to be the bottom of the system. Run the tube up 1m to the window and back down out the window perhaps 3m to a bucket on the porch roof - an easy, simple, working siphon. From that bucket, you can use a regular positive-pressure bottom drain to go down as far as you like.