This section is from the book "Plumbing Plan and Specifications", by J. J. Cosgrove. Also available from Amazon: Plumbing plans and Inspection.
A very good way of specifying materials, when it can be done, is according to certain standards laid down in the specifications. Such a method permits of the widest possible competition while at the same time assuring a standard of goods equal to that called for. It must be borne in mind, however, that under such a specification a more rigid inspection of the goods will be necessary than when they are specified from the stock of a well-known and high-grade manufacturer's catalogue, for irresponsible makers are liable to take a chance on goods which to a casual inspection seem up to the standard, but do not bear a close examination. Such pipe is among the materials which are specified according to standards, and even though the sizes, weights and other properties of soil pipe are generally specified, many manufacturers ship goods that are far from being up to the standards. Extra heavy soil pipe often has considerable below the specified weights, while in other cases it is far from being "sound cylindrical and smooth, free from sand holes and other defects." In large buildings, where many fixtures are to be used, drawings can be made of them if special designs are wanted, or a specification can be made up from a fixture which has already been found satisfactory in use.
A good example of specifying according to standards may be cited in the case of floor connections for water closets and slop sinks. Metal-to-metal connections are now becoming rapidly adopted in practice, likewise flexible bends for connecting water closets and slop sinks to drainage systems. To have to select certain types of floor connections or lead bends for each installation is a difficult matter, and the best way is to specify according to standards. A provision for floor connections which is applicable to all approved floor flanges may be written as follows:
Closets and slop sinks shall be connected to the drainage system by means of adjustable, flexible, metal-to-metal floor flanges. The use of putty, paste, cement or gaskets of any kind in the drainage system is absolutely prohibited.
A section like the following will insure the use of expansion and settlement fittings which will prevent damage to the system or fixtures:
Each water closet and slop sink shall be connected to the drainage system with at least 3 inches of lead pipe intervening between the floor flange and the soil pipe. This lead pipe shall be corrugated with at least two corrugations to make it flexible so it will give under shrinkage or settlement without damage to fixtures.