Referencing my custom control in server side code

This must be simple - like me. I have a custom control that is a dropdown list. It's registered in web.config and renders fine on the page. I'm having trouble trying to get the selected value to use in my server side code. I don't know the id to use. Normally I'd use "myDropdownlist.SelectedValue". What value do I use instead of "myDropdownlist"? I've tried all variations.

 In web config:

<add tagPrefix="MyControls" src="~/Controls/BasketCodes.ascx ...