So, you want to access some content from inside a page that you created from an existing master page?  The most clean way to do this is to create a public property in your master page, then access that.  In my case, I have a search button on a master page that I want to use from inside to pages that derive from that page.  So, Here is how I declare my master page:

   1: <%@ Master Language="C#" MasterPageFile="~/MasterPages/MasterPage.Master" AutoEventWireup="true"
   2:     CodeBehind="ContactMasterPage.master.cs" Inherits="ThreePLogic.Web.ASPWeb.ContactPages.ContactMasterPage" %>
   3:  
   4: <asp:Content ID="Content5" ContentPlaceHolderID="ContentCenter" runat="server">
   5:         <asp:TextBox ID="TextBoxSearchName" runat="server" Width="200px" CssClass="InputText"></asp:TextBox>
   6:         <asp:Button ID="ButtonSearchName" runat="server" CssClass="SearchBtn" />
   7:         </div>
   8: </div>

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