House Traps Fresh-air Connections Drum Traps and Non-syphoning Traps

The house trap is a deep seal trap placed inside the foundation wall, and intersects the house drain and house sewer. The trap is placed at this point for a number of reasons: first, to keep sewer gases from entering the pipes in the house; second, this location is where the house drain ends. This trap should have two clean-outs, one on each side of the seal. The clean-outs should be of extra heavy cast-iron body with a heavy brass screw cap. The cap should have a square nut

or a wrench to tighten or unscrew the cap. This cap should be brought up flush with the floor. When a house trap is being set, it is necessary to set it perfectly level, otherwise the seal of the trap is weakened and sewer gases can enter.

Sometimes the trap is located on the house sewer just outside of the foundation wall. In this case, a pit should be built large enough for a workman to get down to it to clean it out when necessary.

A mason's trap was formerly used to a considerable extent, but is very poor practice to use today on modern work. This trap was built square of brick with a center partition. The brick soon became foul and the trap would be better termed a small cesspool than a trap.

Points to Remember about House Traps.

  1. First, should be a running trap.

  2. Second, two clean-outs.

  3. Third, deep seal, at least 2 inches.

  4. Fourth, set level.

  5. Fifth, set inside foundation wall.

  6. Sixth, accessible at all times.

  7. Seventh, same size as house drain.

  8. Eighth, fresh air should connect with it.


The term "fresh-air inlet" is, as its name implies, an inlet for fresh air. It is placed directly on the house side of the main trap. The connections made vary considerably. A few good connections in common use are explained below.

When the trap is in place, one of the clean-outs can be used for the fresh air. If this is done, a Y-branch should be placed in the hub of the clean-out. The Y-branch should be used for the fresh air and the run should be used for a clean-out.

A Y-fitting can be inserted directly back of the trap and the branch used for the fresh air. An inverted Y makes a good fitting to use directly back of the trap. These branches should be taken off the top of the pipe. The branch taken off for the fresh-air inlet should not have any waste discharge into it and should not be used for a drain pipe of any description.

The fresh-air inlet should run as directly as possible into the outer air, at least 15 feet from any window. The pipes terminate in a number of different ways, some with a return bend, above the ground, some with a cowl cap, some with a strainer. When necessary to run pipe through the sidewalk, a box of brick is made with a heavy brass strainer fitted level with the sidewalk into which the pipe runs. If the pipe is run into the box on the side a little up from the bottom, the possibility of becoming stopped up or filled up is not great. The fresh-air inlet sometimes terminates above the roof of the building.

Special care should be given this fresh-air inlet as it supplies fresh air to the entire system and thus keeps the pipes in a much better sanitary condition.

Sometimes when the house drain is full of sewage, air is pushed out of the fresh-air inlet and disagreeable odors are evident. This is why it should be located as far as possible from any window. Special care should be taken on the part of the plumber not to locate the fresh-air inlet nearer than 15 feet to the fresh-air intake of the heating system.

Fig. 60.--Fresh-air inlet. Fig. 60.—Fresh-air inlet.

When the pipe passes through the foundation wall, the same care should be exercised as with other pipes. That is, if the pipe is 4 inches, a sleeve 6 inches should be cut in the wall for the 4-inch pipe to pass through.

Points to Remember about Fresh Air.

  1. First, never should be smaller than 4 inches.

  2. Second, one size smaller than trap.

  3. Third, location, directly back of trap.

  4. Fourth, leads to outer air.

  5. Fifth, keep away from windows and intake of heating system.

  6. Sixth, always have end of pipe covered with strainer, cowl, or return bend.

  7. Seventh, make as few bends as possible.

  8. Eighth, supplies fresh air to system.


The use of the drum trap is very handy to the plumber as well as efficient and practicable when installed. The trap can be purchased without any outlets or inlets, so the plumber can put them in according to the necessary measurements. The making of these traps with lead is explained in the chapter on Wiping Joints. The open end has a brass clean-out screw on it. When this clean-out screw comes below the floor, another brass screw cap and flange is screwed on the floor above the trap so that the clean-out screw in the trap is easily accessible.

Fig. 61.--Drum trap. Fig. 61.—Drum trap.

These drum traps are called bath traps as they are used mostly on bath wastes. They should never be installed with the clean-out exposed to the sewer side of the trap. In the best practice, heavy brass drum traps are used.


Fig. 62.--Flask trap. Fig. 62.—Flask trap.
Fig. 63.--Clean-sweep trap. Fig. 63.—Clean-sweep trap.

After years of experimenting to produce a trap that would not syphon without venting, we find in use today a large variety of non-syphoning traps. Traps that will hold their seal against all practical forms of syphonic action, or other threatening features, have been made and used and serve the purpose for which they are intended. Various means to prevent the breaking of the seal of these traps are employed. While some depend on a ball or other kind of valve, others rely on partitions and deflections of various kinds. All of these perform the functions for which they are designed, yet the devices employed offer an excellent obstruction for the free passage of waste; therefore, in time, these traps become inoperative. It should be borne in mind that any traps with a mechanical seal or an inside partition are not considered sanitary. The inside partition might wear out or be destroyed and thus break the seal without the knowledge of anyone and allow sewer gas to enter the room. The mechanical device may also be displaced or destroyed, leaving the trap without a seal. If the trap were cleaned out often or examined occasionally, these traps could be used with a greater degree of safety. Some of the forms of non-syphon traps in common use are:

The Flask Trap, Fig. 62. This trap gets its name from its shape. There is an inside wall upon which the seal depends. This trap is like the bag trap, only the two inside walls of the pipe are combined into one. This wall should be of heavy cast brass, free from sand holes.

Clean Sweep Trap, Fig. 63. Some clean sweep traps are dependent upon an inside wall for their seals. They are made of 1⁄2-S, 3⁄4-S, and full S.

Fig. 64.--Mechanical-seal trap. Fig. 64.—Mechanical-seal trap.
Fig. 65.--Standard 'S' trap. Fig. 65.—Standard "S" trap.
Fig. 66.--Bag trap. Fig. 66.—Bag trap.

Sure Seal Trap. The sure seal trap is designed to be non-syphoning. This trap also has an interior waterway. If this waterway leaks, the trap is unfit for use. If these traps are made as shown in the second sketch with the way inside of a larger pipe, it can be detected if the interior wall leaks.

Centrifugal Trap. The centrifugal trap is made similar to the clean sweep, except that the wall of the inlet pipe is entirely separate from the body of the trap. The inlet enters the body of the trap on a tangent, thus making the trap self-scouring which is a good feature.