As already stated, after temperature acclimation which is a must by any method, when going from low Ph in the bag to higher tank Ph, plop and drop is the preferred method.
When the ph of the water in the bag is significantly higher than that of the tank, acclimation of the tank water is preferable.
Rather than going through the hassle of setting up a drip into a bucket, I prefer using a hypodermic syringe in which I pull 20 ml of water out of the tank and inject into the bag. Then I pull 20 ml out of the bag and into what ever container I have available (then down the sink).
The trouble I have had trying to use a drip line and bucket with discus is you lose temperature in the bucket faster than you acclimate the fish to your water.