How to disable warnings in only one project?

Open the Properties of the project and go to the Build page.
Here you will find the Error & Warnings input box
Put the warning number to hide in the input box without the first two letters
If you have more than one warning separate them with colon or semi-colon

(Sorry if labels are not precise, I'm translating from another language VS)

Open project properties. Build > Errors and warnings > Warning level

Select 0 warning level. Details you can read here.

1. In Visual Studio open the project's Properties tab
2. Go to the "Build" tab
3. Set the "Warning Level" to 0

For details on the different warning levels see:

C# Compiler Options > /warn (Specify Warning Level)