Debris Loop for trap primer

The trap primer I'm installing requires a "debris loop"...

As shown here:
http://www.pppinc.net/common_files/images/Trap_Primers/Prime_Rite/PR-500-Installed-W-DU-USS.jpg

If I'm branching off of a vertical piece of 1/2" copper, would it not be redundant?

I'm thinking T and 1/2" ball valve should be fine, the only way I could see creating the loop is using 3 90s...

As a practical matter the trap primers do NOT work as effectively as publicized, but in a vertical line, any debris should be dropping to its bottom and none into the trap primer. It is different with a horizontal line where any sediment would be moving along the bottom and would drop into a TP hanging down from the line.