C# - Bestimmte Zeilen entfernen

public static void removeTrashLines(string mainFile, string trashLinesFile)
        {
            if (Path.HasExtension(mainFile) && Path.HasExtension(trashLinesFile))
            {
                List<string> MainFile = new List<string>(System.IO.File.ReadAllLines(mainFile.ToString()));
                List<string> TrashLines = new List<string>(System.IO.File.ReadAllLines(trashLinesFile.ToString()));
                foreach (string trashLine in TrashLines)
                    if (!MainFile.Contains(trashLine))
                        MainFile.Remove(trashLine);
                System.IO.File.WriteAllLines(mainFile, MainFile);
            }
            else
                Console.WriteLine("File not found");
        }