1. Turn On Power (Near Stamin-Up)

Location:
https://imgur.com/a/rki5LPH

2. Pick up the Shovel (Quick Revive House garage)

Location:
https://imgur.com/a/cLZRIcP

3. Dig up dig piles until you get the Bunker key

Dig Pile Locations:
https://imgur.com/a/spJrhJY

Updated Pile Locations:
https://imgur.com/a/H5q2FAb

The dig piles in PHD Area are only available once you unlock the Bunker Door (Back of Speed Cola House) which the Bunker Door leads to PHD Area

4. Open the Bunker Door (Back of Speed Cola House)

Location:
https://imgur.com/a/yueOQ9W

5. Find a valve part in PHD Flopper Area

Location:
https://imgur.com/a/XsZ7UxF

6. Place valve part here

Location:
https://imgur.com/a/4X3FsKx

7. Find a valve that has yellow lines glowing on the pipe next to it

Valve Locations:
https://imgur.com/a/eTz9mst

8. Lead the yellow lines to the last valve location (Near Jug)

Important Tip: Follow the Pipe

9. Turn the last valve location (Near Jug) last

10. Congrats, you open Pack a Punch

If you don't understand my tips, here's a video from Rustful on How to Get Pack a Punch

Video:
https://www.youtube.com/watch?v=pwBBIBA9KTE

Credit: Rustful