Stomach pumps provide the most direct way to see what trout are actually eating. Below is the safest process for pumping a trout's stomach:

1. Fill the bulb full of water
2. Cradle the trout gently upside down
3. Slide the tube into the trout's mouth and squeeze out the water before sliding it down the fish's throat.
4. Keep the bulb depressed while you gently slide the pump into the fish's throat. Stop when you feel resistance.
5. Let go of the bulb and slide the pump back out. The contents will come with it.