Residential trap primer question

[delta_v]

Hi folks,
Two trap seal primer questions;
My inspector wants a trap seal primer- I've purchased a floor drain with a 1/2" threaded inlet for the copper line to attach to. My question is this; as the inlet for the supply line is just below the flange of the floor drain, should the copper line be run with a slope towards it (in the concrete) vs dropped down along the side of the vertical portion of the drain to run horizontally in the gravel below the insulation? While I'm concerned about it getting stepped on by the concrete guys I am also worried the small amount of water dispensed will be an issue if it's dropped down.

2nd question- In line with the laundry tub, toilet supply or washing machine?
I read a few old posts questioning the use of trap primers in residential settings as the pressure drop may not be enough to trigger the flow. Wondering what will give me most bang for my buck between these three options?
The guys at my plumbing supply were quite insistent, though, that I follow the instructions to allow at least 1' of drop as they've had issues with people returning them when the unit leaks water out the air gap vent so presumably they do work (sometimes, for some people!).
Thanks,
Chris

 

[hj]

A residential installation, because it has smaller pipe sizes, is more likely to operate the TP, than a commercial system with larger pipes and a more stable pressure. However, the only "reliable" ones are those which go inline to a faucet and operate eery time that faucet is used.

 

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[delta_v]

Thanks hj,
Looks like a number of faucets are available with this option; do I need to add a trap primer device in line or simply attach the copper line to the port on the faucet?

Still wondering about my 1st question- should the line be sloped to the drain or can it drop lower to be in the gravel layer?