That's not a bad idea, the baby bath thing.
In my small tank I have to siphon the water in as pouring straight from the bucket would probably destroy everything inside. It's pretty mind numbing, standing there for 5 minutes as water trickles out, lifing the bucket as high as my arms (and siphon hose) will allow to speed the flow up a little.
When changing water in my 180l, Jewel suggest pouring it back into the filter housing in the corner. Not too practical as the housing is in the rear corner so I'd have to stand on steps leaving over the tank with a full bucket aiming for a housing which is about 3 inches wide. Tried it once, seemed to pour more water down the back of the tank than inside. Instead I just pour it in slowly, the guppies seem to enjoy it but they don't strike me as the most intelligent fish in around.