Cowboy, I got bigger testicles by pumping with a Monstertube. You want to go light and you want to pump with the tube filled with water. The way you get air and water out is to use a water proof plastic pump, or you can use just the tube and suck the air and water out with just your mouth and if you get tired, hold the pressure by disconnecting the valve. Drink plenty of water as well and keep it in the tube until you no longer feel discomfort in your testicles. At this point, the water has maxxed your testicles and is going into the sac. If you only want testicles, stop at that point and pull your balls out of the tube and enjoy your bigger testicles. if you also want the sac, you can keep going until you feel bloated and can't go further, then you must work it out of the tube or open the 2 halves up.
Keep doing this daily to keep the testicles pumped and able to accept more volume of semen. Yes, you can increase the amount of cum by doing this because your new testicles can hold more. They are like balloons after all and if you keep inflating and deflating on a daily basis, they will be able to hold more volume each session. They will also remain that size as more semen is produced and held in those melons.