How to seal entry hole for bundle of cat6 cables?

We are in the process of purchasing our first house and once we've moved in I'd like to run cat6 to multiple places throughout the house. I'm estimating about 12 or so runs, maybe less maybe more just depending on how difficult it ends up being. My plan is to drop them down into a central location in the basement where I'll have my server rack.

My plan is to go into the garage and then there's a spot where I can go through the drywall from the garage into the basement. There's only one layer of drywall between the basement and the garage.

Does anyone have any suggestions how I can seal the entry point where the bundle of cables will go through to prevent anything else coming in and out of the hole where the cables are going to be? I can't imagine caulk would work by itself. My current thought is to use a short little piece of conduit that the cables will pass through, like maybe 6 inches or so. Then I'm at a loss as to how I would keep that sealed. Any thoughts?