The pink dig sites are found and used to get extra perk slots.

Golden Shovel
Zombie Blood

How to get the golden shovel: Dig man dig sites about 30 sites and you will here a ding sound and the gray shovel you have will turn golden.

How to get a zombie blood:
1)You can get it from a zombie
2)You can get it from a Panzer
3)You can get it from a dig site
4)If you have the upgraded ice staff, there is 3 flaming wagons around the excavation site(1 by gen 5, 1 by the entrance to no mans land, 1 by gen 4 robots foot)
-Shoot all 3 wagons in about 10 to 15 seconds and if you run up to the excavation site to the right of the pack a punch is a zombie blood and hurry though because it will disappear

When you find the dig site? You will dig it and see a perk bottle, just walk into it, there will be no notification, but when you have 4 perks and you go to get your 5th perk, you can buy your fifth perk.

How can you fuck up getting your fifth perk? Well you could get all 4 perks and get the reward double tap and then when you get the perk bottle you wont be able to get a 5th perk because double tap will be your fifth.

How to get 9 perks? Get 4 other perk bottles from the pink dig sites, and keep hitting up perk a cola til you have 8 perks(not including double tap, if you get double tap from perk a cola, do not take it) then go to the reward box and get your free double tap and have all 9 perks, and if you go down, you will lose all 9 perks, but you can still buy 8 back.

Here is the locations: