Compared to other types of piping joints in the building, the tubular type is usually installed in a less “permanent” fashion. By this, we mean that the components of a tubular drain assembly are more easily disassembled than would be the case in either supply or DWV piping. This is warranted by the need for accessibility in the event of a clog, or because a valuable item has accidentally dropped down the drain of a fixture. With its characteristic use of union and slip joint connections, the tubular system is relatively easy to open for such needs.
Types Of JointsWe tend to generalize the facts concerning such connections, often thinking that tubular goods are synonymous with “slip joints.” True, some components do use this connection method, but others connect in other ways, and you have to know the difference if you want to meet your customer's need in one try. Here then, are the variations you will find in connection means used with tubular goods components:
Slip Joint: This is a method of joining that brings the mating components together in a “telescoping” relationship. A threaded nut on the female end compresses a gasket ring around the inserted male tube end when tightened, resulting in a watertight seal. While it does not provide an extremely strong mechanical joint, the seal is adequate for non-pressurized applications. Another characteristic of such a joint is that it is extremely “forgiving” in terms of dimensional exactness. Because the connection is a telescoping one, it is possible to be off in the length of the male component (as long as the measurement is off in the direction of the “long” side), and still be able to make up the mechanical joint.
Union (Washer & Ground Joint Types): If you understand the concept of a union connection in a supply fitting sense, you should be able to grasp what we have here in a tubular version. Unlike a slip joint, this type of connection provides a tighter, more mechanically secure attachment of components. In this case, a nut catches the shoulder of one component, drawing the joint tight by screwing onto the threads of the other component. There are two basic types of union connection available with tubular lines, most commonly called the “washer” and the “ground joint” types. The washer type of union involves the mating of two flat surfaces that “sandwich” a gasket between. The ground joint type is really very similar to a supply union - the end of one component has a spherical shape that relates to a mating socket on the other. Both types are drawn tight by means of the nut provided.
-- Threaded: Certain tubular components are made with threaded connections for making joints to threaded waste fittings (to link the trap components with the DWV system).
-- Solder (Sweat): This type is used to connect to a copper DWV system.
-- Solvent Weld: This is used in connecting to a plastic DWV system (must be a like plastic material).
Basic Component ConfigurationsGiven the above explanation of connections, we can move onto the various specific components within the category of tubular goods.
Tailpiece: The tailpiece is the component that attaches in “union” fashion directly to the strainer assembly of the sink. It has a flange on the top that is caught by the lower nut of the strainer, sealing it against a sandwiched gasket.
Trap: When the word “trap” is used with a tubular line, it usually means more than one part: a “J” bend, a connecting waste arm or elbow, and sometimes, a flange for the wall or floor. In other words, a tubular trap is not a “part,” it is a set of parts - an assembly. The type of arm or elbow supplied determines the basic type of trap it is - “P,” “S” or “sink.” The first two versions get their names from the alphabet letters they resemble. In function, the “P” trap connects to a stack or waste line back in the wall, whereas the “S” variety routes the water down through the floor to connect to the DWV system somewhere below. In general practice, the “S” type is not allowed by most codes today, since it does not provide as good a venting capability as the “P” type. The arm used with either of these first two types of trap is typically attached to the “J” bend by means of a union connection. The third basic style of trap, called the “sink” type, looks like a “P” trap with a short waste arm. Actually, the sink trap uses an elbow, rather than a tubular arm, that attaches to the “J” bend as either a washer or ground joint union. (Note: though its name would seem to indicate otherwise, the sink trap is not broadly used for sink installations - it is geographically specific to certain localities.)
Waste Connection: The final component in our linkage of the sink to the waste line is called a “waste connection,” or - more typical of the plastic tubular lines - “trap adapter.” In most cases, this component has a slip joint connection on one end, with a threaded, sweat or solvent weld connection on the other. In other words, this part makes the transition from the type of connections used with tubular components to those connections used with the waste line of the DWV system. On the waste line side of the fitting, there are a variety of connection options available. For threaded joints, there are male and female versions (some manufacturers offer a multi-purpose connection that provides male threads on the outside of the connection, and a female solder socket on the inside, thus making it usable for threaded or sweat connections). In plastic versions, there are types that provide a slip joint connection on one end, and a solvent weld provision on the other. There are also versions that provide a solvent weld connection on both ends.
Continuous Waste: When a double compartment sink is involved, one trap can handle both, but the drainage from those two must be brought together to enter that trap in common.
This involves an assembly of parts called a “continuous waste” that consists of the waste tee and, depending on the specific layout of the drainage system, one or two waste arms.
Branch Tailpiece for Connecting Dishwasher: Since it is common to feed the discharge line from a built-in dishwasher into the basic drain system under the sink, there is a need for a different fitting to receive this tie-in. The fitting used is a special version of a tailpiece that includes a side inlet nipple for connecting either a hose or copper tube line from the dishwasher.
Other Components: In addition to these most common tubular components, there are others to be aware of, including extension tubes, threaded tubes, slip connections and offsets (see manufacturer catalogs for more details.)
Materials-- Brass: Brass tubular goods are made of relatively thin-wall extruded material that is most often chrome plated. (As a rule, brass drain material installed outside the wall is chrome plated; that which is installed inside the wall - such as bath wastes - is unplated.) Brass tubular lines are offered in three common weight grades, designated by the gauge of the metal. In this case, contrary to what you might tend to assume, the gauge number gets higher as the metal gets thinner. Thus, with the selection of 17, 20 and 22 gauge tubular components, 17 represents the heaviest (thickest) grade, 22 is the lightest (thinnest). In addition to tubular brass construction, there are also components that are made of cast brass. These have heavier wall sections than the tubular variety.
-- Plastic: The three types of plastic material used in tubular goods lines today are: ABS, PVC and PP. These materials are progressively more resistant to chemical attack in the order shown, with PP being the most resistant.