In order to get this achievement you'll need to buy a silo, and then all of the upgrades for it. Those prices are as follows...
Silo (450 n):
2nd port - 500 n
3rd port - 575 n
4th port - 650 n
Total - 2175 newbucks
Note: As Pete5683 says, you can fill more than one slot with the same item. It'll still count!
1.2.1 update: This update added the capacity limit per slot to 300, and added 3 slots per side of the silo, making the overall requirement 3600 units of items to fill the silo. This makes the achievement more grindy, but can still be accomplished with the same technique below. To speed the process though, you can also add the excess fruit from your crops to the process.
After you've got the maximally upgraded silo, you'll need to put
300 of an item in each of the
twelve ports (
300 carrots,
300 pink plorts, etc.). The easiest thing i'd suggest for this is to follow my guide for selling 5,000 plorts
Once you've gotten things rolling for that achievement, start storing each of your four different plorts in the four ports of the silo until all ports are full. Afterwards you can sell all the plorts to continue Plort Tycoon. Another achievement in the bag!
Here's my video for all achievements if you'd prefer. Skip to 13:13 for Burstin' at the Seams.