Welcome to health care magic.
1.There is minimal amount of free fluid in side the tunica ( scrotal sac) which is normal. If its excess its called
hydrocele.
2.You said you are feeling some mass of ping pong ball size - generally nothing should be felt other that testicles - probably the
epididymis and chord what you are feeling within the
scrotum.
3.The chord is generally irregular on palpation.
4.Inthis case if you feel any thing suspicious in the scrotum, you need to see your GP , let it get examined and see any abnormality is there, if so an
ultrasound is indicated.
5.An ultrasound is good tool of investigation for the scrotum, testis, chord, epididymis and vessels and free fluid. Good luck.
Hope i have answered your query.
Any thing to ask do not hesitate. Thank you.