Most likely it has a blown seal.
Most "PUMP" air guns use the for-arm (Forward Handle) to pump the air gun.
One that you have to manually pump the forarm up to build enough pressure in the air tank to fire the gun.
A pump action BB gun requires you to pump the forearm (The grip under the barrel) several times to store air in the air tube. This air propels the pellet when the trigger is pulled.
with a hand pump
Pump powered air guns should only be pumped when you are ready to shoot the gun. Never leave an air gun pumped for a long period of time it is very hard on the seals and will eventually ruin them. It has been recommended that on a multi pump rifle or gun that you only pump it once to keep the chambers closed when you store it.
Hold the gun with the barrel pointed in the air and with your finger off of the trigger. It is best to hold it in a holster.
pump-charged gun
Multi pump air guns have an on-board air chamber that requires you to pump the forearm several times to fill the air chamber before you shoot. You can vary the power by the number of pumps.
Where do I buy Benjamin Air rifle repair parts? Model 310 and 310
Fifty caliber, but it is more of a toy than a paintball gun.
Most likely a broken seal.
You will need to connect the air. Professor to the water pump. The air going into the well will force the water upward.