I would be really cautious about using any soap substance on a parakeet. I was just at the vet with Pinto for her tumor, and we got to talking about cleaning cages. The vet agreed completely with never using soap on a cage, just water with a tiny amount of bleach.
You would never wash your *parakeet* with bleach
So for parakeets I think warm water should be enough.
What did you want to add shampoo for? Is your keet particularly dirty?