I also do this, put the water directly from the tub to the aquariums by a hose. Before of trying this, I used to carry on my back 40 times a bucket of 5 gal. when I changed the water of the aquarium. Since I do 30% waterchange in all aquas weekly, I used to loose all saturday and sunday on this.
The secret is to add the necessary amount of dechlorinator (I use Seachem Prime Pond) calculating the right quantity for the whole aquarium before (2 mins) and then add the water. While adding, put another dosis of the dechlorinator and then wait.
The first time I did this I was very nervous and did all the tests, but since you had added the dechlor. in the water before, it works immediately with the water added, and any chlorine is detectable. I have nine aquariums, going to ten next month, and this method made my life very easy and relaxed.
During two weeks I measured ammonia, nitrite and nitrate of all my aquariums daily after used this method and nothing changed, neither in the first day after waterchange.