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You are an expert at summarizing long articles. Proceed to summarize the following text: 
TECHNICAL FIELD 
     The present invention relates to a deodorization device, and more particularly to a passive deodorization device suitable for use with a portable toilet having a vent tube extending from a holding tank. 
     BACKGROUND OF THE INVENTION 
     Portable toilets in self standing enclosures or found in the transportation industry have a seating area disposed above a holding tank. A vent tube extends from the holding tank to vent the holding tank to the atmosphere. This vent tube often passes through the enclosure to vent the holding tank through the enclosure top. Malodorous vapors emanating from the holding tank foul the air in and around the enclosure. 
     One method of masking the odor inside the enclosure includes mounting an air freshener, which releases a pleasant aroma, to an interior enclosure wall. This particular method does not solve the odor problem outside of the enclosure. Furthermore, after an extended period of time inside the enclosure, the spent air freshener must be manually replaced. A users hands may become soiled when removing the spent air freshener assembly or exchanging the spent air freshener element inside a housing. Furthermore, the air freshener may be removed prematurely by an enclosure visitor, subjecting subsequent visitors to the malodorous vapors associated with the toilet. 
     SUMMARY OF THE INVENTION 
     The present invention provides a passive deodorization device suitable for use in a portable toilet enclosure having a vent tube for venting odors from a holding tank. The deodorization device has a housing with an engagement surface for engaging a vent tube outer surface, and an aperture. Two fingers extend from the aperture into the vent tube. A retention member mounted on the fingers engage a vent tube inner surface and clamps the vent tube wall between the housing and retention member. A deodorizing element slipped into the aperture between the fingers deodorizes the malodorous vapors associated with the toilet. 
     A general objective of the present invention is to provide a deodorization device capable of treating malodorous vapors inside an enclosure and exiting a holding tank vent tube. This objective is accomplished by providing a device which is inserted into the vent tube through a hole formed therein which passes through the enclosure. This allows mounting the device in the vent tube from inside the enclosure exposing the deodorizing element to the air inside the enclosure and the vent tube. 
     Another objective of the present invention is to prevent the easy removal of the deodorization device once installed. This accomplished by providing retention members which are self-locking and, thus, prevent device removal from the vent tube. 
     Still another objective of the present invention is to provide a method for easy replacement and disposal of a spent deodorizing element. This objective is accomplished by providing a housing having an aperture, and fingers extending therefrom to hold a deodorizing element. The spent element is replaced by inserting the replacement deodorizing element into the aperture; forcing the spent deodorizing element out of the grasp of the fingers, and allowing the spent deodorizing element to fall through the vent tube into the holding tank. 
     The foregoing and other objects and advantages of the invention will appear from the following description. In the description, reference is made to the accompanying drawings which form a part hereof, and in which there is shown by way of illustration a preferred embodiment of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of deodorization device incorporating the present invention installed in a vent tube; 
     FIG. 2 is a schematic cross sectional view of the deodorization device and vent tube along line  2 — 2  of FIG. 1; 
     FIG. 3 is a perspective view of the deodorization device of FIG. 1; 
     FIG. 4 is a schematic cross sectional view of the deodorization device along line  4 — 4  of FIG. 3; and 
     FIG. 5 is a side view of the deodorization device of FIG.  1 . 
    
    
     DETAILED DESCRIPTION 
     As shown in FIGS. 1 and 2, a passive deodorization device  10  attaches to a vent tube  12  for a portable toilet compartment. The vent tube  12  extends from a holding tank (not shown) disposed beneath a seating area of the toilet compartment through the toilet compartment interior and exhausts to the outside. Malodorous fumes originating in the holding tank flow through the vent tube  12  and exhaust into the atmosphere. The passive deodorization device  10  snaps into an opening  14  bored in a wall  15  of the vent tube  12  to treat the malodorous vapors associated with the portable toilet in the vent tube  12  and toilet compartment. 
     The passive deodorization device  10  has a housing  16  with an aperture  20  formed therein, and fingers  22  extending from the aperture  20  for holding a deodorizing element  30 . The housing  16  engages an outer surface  18  of the vent tube  12  with the fingers  22  extending through the vent tube opening  14  in the vent tube interior  24 . The fingers  22  have self-locking members  26  which engage a vent tube inner surface  28  and cooperatively clamp onto the vent tube wall  15  with the housing  16  to secure the deodorization device  10  in place. A deodorizing element  30  slipped into the housing aperture  20  is grasped by the fingers  22 , and contains agents to neutralize malodorous vapors associated with the portable toilet. Preferably, the deodorization device  10  is formed from molded plastic, such as polyethylene. 
     Looking particularly at FIGS. 3-5, the cup shaped housing  16  defines a cavity  32  and has an exterior convex surface  34  and an interior concave surface  36  joined together by an edge  38 . The housing edge  38  conforms to and abuts the vent tube outer surface  18  to cooperate with the self-locking members  26  and hold the housing  16  in place. A substantially rectangular aperture  20  formed in the housing  16  has opposing long sides  40  joined by opposing short sides  42 , and is sized to receive the generally rectangular deodorizing element  30 . A lip  44  formed on the aperture sides  40 ,  42  extends toward the aperture center to inhibit removal of the deodorizing element  30  through the housing  16 . Vents  45  formed in the housing  16  expose the deodorizing element  30  in the housing  16  to air inside the toilet compartment interior. Although a rectangular aperture  20  is shown and described, any shape aperture may be used, such as a round, square, polygonal or the like, depending upon the shape of the deodorizing element  30 . 
     The pair of opposing fingers  22  cooperatively retain the deodorizing element  30  and expose it to the malodorous vapors associated with the portable toilet. Each finger  22  has a proximal end  46  formed as an integral part of the housing  16  and extends from the housing aperture short sides  42  through the cavity  32  toward a finger distal end  48  disposed in the vent tube  12 . Each finger  22  has an interior side  49  which engages an opposing side of the deodorizing element  30  to cooperatively grasp the element  30 . Ribs (not shown) may be formed along the length of the interior finger side  49  of one or more fingers  22  to improve the grasp on the deodorizing element  30 . 
     Inwardly extending stops  50  formed on the finger distal end  48  interior side  49  inhibit the deodorizing element  30  from being pushed too far through the housing aperture  20  and into the holding tank at the bottom of the vent tube  12 . An exterior side  56  of each finger  22  has a self-locking member  26  formed thereon to engage the vent tube inner surface  24 . Although two fingers of equal width are shown and described, one finger may be wider than the other to provide protection for the deodorizing element from the elements, such as rain, which may enter the vent tube. 
     A pair of opposing walls  58  join the finger proximal ends  46  to form a shaft extending generally perpendicularly from the housing aperture  20  into the cavity  32 . The shaft walls  58  guide the deodorizing element  30  between fingers  22  extending into the vent tube  12 . Preferably, the walls  58  have a tapered portion  59  extending toward the finger distal ends to guide the deodorizing element along the length of the fingers  22 . Although the shaft is shown and described as having a smooth interior surface, ridges (not shown) may be formed on the shaft walls  58  to engage the deodorizing element  30  and prevent it from inadvertently slipping out of the fingers  22  and down into the holding tank. Vents (not shown) may also be formed in the walls  58  to increase the exposure of the element  30  to the air inside the cavity  32 . 
     The self-locking members  26  are formed as an integral part of each finger exterior side  56  and engage the vent tube inner surface  28 . Each self-locking member  26  has a ramped surface  60  which causes the fingers  22  to deflect inward when passing through the vent tube opening  14 , and a locking surface  62  which engages the vent tube inner surface  28  when the ramped surface  60  has passed through the vent tube opening  14 . The ramped surface  60  has an increasing depth as it extends away from the finger distal end  48  to deflect the finger  22  inward. The locking surface  62  is substantially parallel to the vent tube inner surface  28  and is formed at the end of the ramped surface  60  having the greatest depth. 
     Referring to FIGS. 2,  4 , and  5 , the self-locking member locking surface  62  cooperates with the housing edge  38  to clamp the vent tube wall  15  therebetween and hold the deodorization device  10  in place. Advantageously, the self-locking member  26  prevents easy removal of the deodorization device  10  from the vent tube  12 . However, other retention members for securing the device  10  to the vent tube  12  may be used without departing from the scope of the present invention. For example, ribs formed as part of the finger exterior side  56  to providing a friction fit may be used when the vent tube wall thickness is not known, without departing from the scope of the present invention. Other retention members, such as screws, bolts, adhesives, or the like may also be used to mount the deodorization device  10  to the vent tube  12  without departing from the scope of the present invention. 
     The deodorizing element  30  is an article composed of materials impregnated with agents known in the art. Preferably, the element  30  is biodegradable, such as recycled textiles and paper held together by a binder. The materials are formed into a brick shape having a cross section which slips through the housing aperture  20 , and then impregnated with the deodorizing agents, such as natural aromatic oils to mask or neutralize the malodorous vapors associated with the toilet. 
     Looking back at FIG. 2, the deodorization device  10  is installed by boring an opening  14  having a diameter approximately equal to the distance between the finger exterior sides  22 , into the vent tube wall  15 . The fingers  22  are then inserted into the vent tube  12  through the opening  14 . As the fingers  22  pass through the vent tube opening  14 , the self-locking member ramped surfaces  60  formed on the finger exterior side  56  cause the fingers  22  to deflect inward. Once the ramped surfaces  60  pass through the vent tube opening  14 , the fingers  22  spring outward causing the locking surfaces  62  to engage the vent tube inner surface  28  and clamp the vent tube wall  15  between the locking surfaces  62  and the housing edge  38 , thus locking the deodorization device  10  in place. Preferably, the deodorization device  10  is oriented such that the fingers  22  are vertically aligned in the vent tube  12  allowing the lower finger  22  to support the deodorizing element  30 . 
     The deodorizing element  30  is inserted into the housing aperture  20  to complete the assembly of the deodorization device  10 . Preferably, the deodorizing element  30  is forced through the housing aperture  20  and past the lip  44  formed on the aperture sides  40 ,  42  to prevent removal of the element  30  back through the aperture  20 . Most preferably, the deodorizing element  30  is slipped along the fingers  22  until it abuts the stops  54  at the finger distal ends  48 . 
     Referring to FIG. 2, once deodorizing element  30  has been exposed to the malodorous vapors for a period of time, the spent deodorizing element  31  must be replaced in order for the deodorization device  10  to remain effective. The spent deodorizing element  30  is replaced by inserting a fresh deodorizing element  30  into the housing aperture  20 , forcing the spent deodorizing element  31  out of the grasp of the fingers  22  and into the vent tube  12 . The spent deodorizing element  31  is allowed to fall through the vent tube  12  and into the holding tank for disposal with the holding tank contents. 
     While there has been shown and described what are at present considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention defined by the appended claims.

Summary:
The present invention provides a passive deodorization device suitable for use in a portable toilet enclosure having a vent tube for venting odors from a holding tank. The deodorization device has a housing having an engagement surface for engaging a vent tube outer surface, and an aperture. Two fingers extend from the aperture into the vent tube. A retention member mounted on the fingers engage a vent tube inner surface and clamp the vent tube wall between the housing and retention member. A deodorizing element slipped into the aperture between the fingers deodorizes the malodorous vapors associated with the toilet.