Dear Michelle
I just thought that I would let you know that it is almost impossible to search the Manchester 1841/51 census for any family without an address, as there is no name index. The 1851 is also corrupted by water damage and in parts it is impossible to read the transcripts.
Your best option is to ask if anyone has been researching Platt's in Manchester, as they may have extracted all the Platt names, or alternatively find them on the 1861, and hope that they are still at that address in 1851!.
Pat