Much of the problem is that cable that has been wound on a drum can do some strange things when pulled off the reel.
theoretically it should unreel straight, but it has its own ideas, especially this time of year.
Never. That ‘civil’ duct is corrogated. Your cable end will dig in. The draw string is there for a reason.
anyway, all this is (as usual) somone trying your make an everyday simple process into a complicated one.
OP. Drop your duct in the ground, make sure the draw string is there, pull the SWA in once the spark has confirmed the size you need.
Simples!