There was some script for dropping tanks same way in editors depot, I think thats one of the tutorials, written by David Berka. But the idea is
; script by David Berka (David.Berka@nmi.at), modified by -=Ronin=- Uldics
_heli = _this select 0
_tankuliste = tankulisteW
_palikusietanki = count _tankuliste
heloreadyW=false
#Saakums
@ not heloreadyW
_car = _tankuliste select (_palikusietanki-1)
#Update
_heliPos = getPos _heli
_heliPosX = _heliPos select 0
_heliPosY = _heliPos select 1
_heliPosZ = _heliPos select 2
_car setPos [_heliPosX, _heliPosY, _heliPosZ - 5]
_heading = getDir _heli
_car setDir _heading
~0.01
? (not heloreadyW) : goto "Update"
_chute = "Parachute" createvehicle [0,0,300]
#Drop
_chute setDir _heading
~0.01
_carPos = getPos _car
_carPosX = _carPos select 0
_carPosY = _carPos select 1
_carPosZ = _carPos select 2
_chute setPos [_carPosX, _carPosY, _heliPosZ - 18]
#DropUpdate
_chutePos = getPos _chute
_chutePosX = _chutePos select 0
_chutePosY = _chutePos select 1
_chutePosZ = _chutePos select 2
_car setPos [_chutePosX, _chutePosY, _chutePosZ - 3]
~0.01
? (_chutePosZ > 3) : goto "DropUpdate"
_palikusietanki=_palikusietanki-1
? (_palikusietanki>0) : goto "Saakums"
I have modified it to suit my needs of dropping few tanks, one at every arrival.
heloreadyW is used to get to know, when the helo is at which waypoint (addtank or droptank).
@ not heloreadyW is used to wait for helo to arrive at one of the waypoints.