If you are looking to do schematic layouts there are several ways to do it. First you can simply sketch the diagram using drawing, but there is no associativity . You can also use Pro/Diagram which is really for Pro/Cabling but makes nice piping diagrams as well. The PTC solution for your problem is called RSD or Routed System Designer which will do many different types of diagrams such as piping and cabling.
If you are looking to do full 3D solid modeling of a piping system then you really need Pro/Piping. If you don't have Pro/piping and are creating a small set of piping you could create the pipes as sweeps along datum curves which were created thru points. The points being the bend locations.
RSD is the new diagramming tool and very capable of creating P&ID's. It will drive Pro/PIPING via an XML interface. Once you have imported the XML file into piping you will get a list of pipelines, equipment and fittings, once you designate your equipment the RSD info will allow you to select a pipe to route. Once you have selected the pipeline the equipment that you are routing from and to will highlight, all you have to do is define the path. Once you have defined the path the RSD xml info will then tell you what fittings should go in the pipeline. Very Very powerful