This post is a reference material.
Made 2 set of siphon for a person in Australia. It is a 25mm Siphon kit, with double elbow or high water "Whistler" outlet for both. This post is to give simple instruction on the slight differences in its assembling.
Above on the left is the double elbow and right the "Whistler". Double elbow is a straight forward type of outlet, where as the whistler is slightly more complex.
One different that is on the final down spout, it is reverse for the Whistler more holes on top as compare to the Double Elbow with holes towards the end of outlet. This doesn't matter much but this is how I would recommend it.
Apart from this difference, the Whistler use a Tee joint as the second elbow replacement, this Tee is the one that does most of the aeration while water level is high.
The first vertical, the one immediately after growbed can be adjusted to length depend on your installation. Extra 25mm tubing provided just cut to length. This standard is shown using 3" of 25mm tubing. The horizontal link after the elbow is also 3" in length. Normally this don't required to be adjusted.
The aerator tip is provided to give additional aeration while water is high. This tip adapter has a marking to be align with Tee joint mark to ensure optimum aeration. Once fix, its can be glued on to prevent leak (not critical)
All fittings not glued, only the aerator tip adapter is glued on to prevent difficulties in doing it right. This outlet has been tested and work good. The Whistler is tested by using a non holed pipe as in first photo to ensure it can give optimum aeration even with high water situation.
Whistler should work, aerating water up to minimum of 8 inches clearance between your growbed base to highest water level in the tank.