Careful with your "ciphering" there when you're using large animal drugs "off label". The dose of fenbendazole for dogs is 50mg/kg, so your 20kg dog needs 1000mg per dose or 1 gram. The tube of horse wormer is 25g or 25 doses for your dog.
125ml is not 5x the 25g tube of paste. ml do not equal g if you don't know the mg/ml or the mg/g
the 125ml goat dewormer is a 10% solution or 100mg/ml so you're getting a total of 12,500mg or 12.5g or 1/2 the amount of the horse tube, but in a much easier format to dose your dog