Anti siphon valves fo wvo

[cur.bill]

On my 1993 F350 IDI I have installed 2 new fuel tanks hooked up with 2 electric fuel pumps. I have a manual return line under the seat and I am trying to decide where to install anti-siphon valves. I have 2 seperate filter heads emptying into a brass tee into my IP. One filter head is fed thru a HE. The other is clean and not wrapped or anything. The diesel head will get the AS valve before the head but I am not sure where to put the valve????? Thank you

 

[gearhead]

is the "anti-siphon" valve a drainback valve so fuel doesn't return to the tank when off?

 

[cur.bill]

They are one way valves which open under pressure and when not under pressure prevent a siphoning action. The diesel line will have the valve before the filter head so that I will not lose prime in the filter but I am wondering where to put the valve for wvo usage. Before the head or after the head and before the tee to the IP.