The waste connectoin underneath the bath is leaking (it is a combined O&W with a remote operated plug).  On disassembling it I found it did not have a washer.  Is it possible that it was designed not to need a washer?  Some of these units that I have seen just use a plain washer but those just seem to fit flat on the underside of the bath.  In my case, the female unit underneath the bath has a cup shape, whilst there is a male fitting under the waste grill/plug assembly so there would only be a limited space for a washer.  Maker is not known. I hope someone can recognise what I am talking about from my description.  Do you think I need to fit a washer to this?