Bathroom fixtures would cover the washbasin (GB) / sink (US, but becoming more common in GB) , toilet, shower, bath etc, and possibly also smaller things like towel rails. There is a distinction between 'fixtures' and 'fittings' which is sometimes, but not always, followed.
Pipes, drainage and suchlike are 'plumbing'. They are generally 'behind the scenes'. 'Bottle-trap' would certainly count as plumbing, but it's not an everyday term - only plumbers and very enthusiastic DIY folks would know what it was.