The function of mud gun in a solids control system is agitating and transferring. Usually it works together with mud agitator, the main body of mud gun is in the bottom of the tank, same with mud agitator shaft. Mud gun pipeline can be used to transfer mud from one tank to another. Its power come from mud pump pressure and jet mud mixer pressure. 
Check the photo below for the mud gun, mud agitator and various pipelines in the tank bottom. The mud gun is operated by butterfly valve or gate valve installed on top of the mud tank.