DWV fittings for the system are different from those for water supply pipes, even if they look the same.  For one thing, DWV pipes are usually larger and the inside surface of the pipes fit flush with the inside of the mounting.  This design allows for the smooth flow of material over the joint.

DWV fittings have also, “direction” built into them; they can only be installed on one way so that waste and water only flows one way (as long as there is a correct slope).  The corners in DWV fittings are not the same as the nominal angle of the bend.  For example, if you need a 90 degree change in direction, the Assembly is actually something more or less in order to take account of the slope.

Fittings differences in material, the pipe size and shape.  In spite of dozens of variants, you need to know only a handful.  However, it is still important that you have the correct Assembly for every situation, because where 2 or 3 types can actually apply, only one is the correct type.

The 1/4 inch bend (or 90 degrees bend) and the sanitary tee (both single and double rooms models) are used where changes the direction of flow from horizontal to vertical.  This is the only situation where codes allow these fittings.

When the flow direction of vertical to horizontal, you must help pieces that use a gradual curve.  For this situation, learning about long sweep 1/4 inch bends and the combination Y-branch.  You will negotiate corners using 1/6 curves, 1/8 curves, 1/16 curves or 45-degree-Y.

Use fittings with the most gradual curves as a pipe direction at the same horizontal plane changes.  The closet turn for toilets is an exception.  The closet bend must fit within the floor joists, so that the codes don’t require a sweep, or oblong, mounting.

In all cases the size of the Assembly must match the size of the pipes that connect.  In some fittings of the sale points all the same size, and in others they vary.  You can switch adaptors the size of an outlet on a smaller size, if necessary.

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