This is important if anyone wants to use their reserve slot in the future :

With the increase to 25 slots, the server still shows 24, this is because the 25th slot is hidden. Any normal player browsing will see 24/24 and think the server is full up. This is good because previously people would join the server get all the way in, and then get booted by the reserved slot system, this prevents that and keeps casual browsers happy

Now, in order to connect to the server you have to first actually be in TF2, you cant do it from the steam server browser window if the server is at 24/24. You have to open the console and type 'connect 8.12.20.112:27015' this will override the game not letting you connect. When you get in the plugin functions as normal and kicks the person with the lowest connected time not on the list.
To reiterate you
MUST CONNECT MANUALLY if the server is full:
1) Start TF2
2) Open the Console
3a) type connect 8.12.20.112:27015 (server #1)
3b) connect 18.243.2.105 (server #2)
3c) connect 217.115.196 (server #3)
In order to get your Steam ID, you need to take the following steps
1) Enable the developer console, go to options, keyboard, advanced, check the box, the key is ~ by default
2) Join any TF2 server
3) Open the console and type 'status', this will display your steamID which looks like STEAM_0:0:12345
4) Copy the ENTIRE THING, and paste it here