What you're asking for suggests a design flaw. If the CheckBoxes are displaying an indeterminate state then that means that the values they are bound to are not True or False but null. If you don't want your CheckBoxes to indicate the existence of null values then why do you have null values in the first place? Why does it make sense for the database to contain null values if it doesn't make sense for the application to show these null values.

I really think that you need to address this. I would think that you need to change your database schema to disallow nulls in those columns and then you need to make sure that any new records always have a value in those columns, either by setting them explicitly EVERY time or else by setting a default value on the columns.

Now, CheckBoxes can only display an indeterminate state if you have their ThreeState property set to True. Presumably you have dragged these columns from the Data Sources window to create the CheckBoxes. The reason that their ThreeState property has been set to True is SPECIFICALLY so that they can indicate that the bound value is not True or False.