Brick dust will kill worms off in a hurry; you toughen ("scour", in the old books) them up in sphagnum moss.
Squatts are supplied in foundry sand, but I've no idea why!
I've just checked in Benny Ashurst's book; he gives quite a lot of info. Lancashire breeders used foundry sand because they had foundries; any damp sand will do. On the day, seive them off and put into a little dry or barely dampened groundbait. As for feeding with them, he says he could ball in half a gallon in just seven pounds of groundbait, because they can't break the ball up in mid-air like standard hook maggots can.