Step 1. Set your primary DNS server to the address at the top of this page in the WFC settings.
Make sure to change the settings for the correct connection (under advanced settings if using WPA) and hit "Save Settings".
This has to be done here: https://www.pokecheck.org/i/howto.png
Step 2. Make a deposit request for the Pokémon you want to check. When asked for what Pokémon you're looking for, enter anything.
When you confirm the offer, the game will tell you your Pokémon can't be traded (but it has been recorded on Pokécheck).
If for any reason your Pokémon is accepted, you are on the official GTS and you didn't follow step one correctly, make sure
you're setting up the right connection (check advanced settings if using WPA). This script can tell you if your ISP is blocking Pokécheck.
In generation 5, you should get error code 13266
Normally after these steps your Pokemon should be visible on Pokecheck however you must use the same IP you used to deposit your Pokemon in the GTS