A plastic bin, out of direct sunlight, filled with rainwater or if you use tap water make sure it is treated with Reptisafe (Amazon.com carries it too). Spring Water will do too but never Distilled, never untreated tap water. Tadpole food from Walmart, or lettuce that has been softened by gentle boiling is excellent. Tadpole food is best because it sinks thus eliminating the potential for air bubbles to get in the stomach of the tadpoles. If you keep them outside, remove any water insect you don't recognize, especially dragonfly larvae (pull up picture on computer to recognize) - they will eat the tadpoles. Every year I remove several hundred from my rain barrels and raise them outside with no problems, except Wolf Spiders and Dragonflies that wait on the artificial lily pads. If you can find a nearby pond with quiet water, it is probably best to deposit them there. Should you decide to keep a few, you are indeed in for a treat. Their development is a study in wonder. Be sure and read the Care Sheet of Grey Tree Frog on Frogforum.

If you have them in a bowl, an aquarium air stone will provide oxygen until they are froglets. Air stones can be found at Walmart, pet stores or Amazon.com. Nothing expensive. GoodWill Thrift often has aquarium supplies. I have used a Turkey Baster for removing poop. Turkey Basters are at the grocery store; it's a long plastic tube with an opening on one end and a bulbous hand pump on the other.