The following list Plumbing Industry Resources websites provide the architect with helpful technical resources. For plumbing related articles, visit the plumbing page at archtoolbox.com.
Plumbing & Drainage Institute
The Plumbing & Drainage Institute is an association of manufacturers of plumbing and drainage products. Their website includes a series of publications that include information of designing grease interceptors and, most helpful to architects, a list of the minimum space requirements for in-wall plumbing fixture supports.
American Society of Plumbing Engineers
The ASPE is the international organization for professionals skilled in the design, specification and inspection of plumbing systems. They sell a number of technical publications and they also sell some very helpful webinars.
Plumbing Manufacturers International
The Plumbing Manufacturers International's website is called SafePlumbing.org. The website includes some helpful resources, including a listing of various markings that can be found on plumbing products.