I review P&ID for RCRA sites all of the time. You don't state what your problem is, so it a little hard to figure out what you want. If you want to know the symbols used, I'd do a a Google search on them.
Most P&ID drawings are not necessarily drawn to scale as they're normally showing how the tanks are connected and not necessarily a top down view of the containment system with the piping layout actually shown. It can be done this way, but can get very confusing if you have pipes crossing each other. Color coding your pipelines will make it easier to understand processes.
In some P&ID they'll show a artificial side view of the tank system (i.e., tanks, ancillary equipment, secondary containment systems). Normally you'll at least try to identify all of the individual pumps and tanks. Depending on the detail of the P&ID, you may need to show every piece of pipe (Some EPA regulations require this to identify every potential source of emissions (e.g., RCRA 40 CFR 264 Subpart BB).
