When filling the siphon I placed a cap on the bottom end and braced it with a big rock. Make sure you brace it good - once I filled the siphon with 25 buckets of water and just as I was going to put the top cap on the bottom one came loose, meaning I had wasted all that work of lifting 25 five gallon buckets of water and pouring them into the siphon.
Different dams may need different angles on top. You can get 45 and 90 degree angles and can use the 45 degree ones at angles to make more or less of an angle.
This view is looking down the pipes from the top of the dam. You can see I needed a short 2 foot piece of pipe as well as one full length of 10 feet to go across the top of the dam. This, too , will vary with dam width. You get some length from the tee and the angle. You may have to cut the pipe to fit.
