ANTICORROSIVE FLANGE SYSTEM FOR SANITARY CUPS BACKGROUND OF THE INVENTION. A. FIELD OF THE INVENTION. This invention relates to flanges for sanitary cups and, more particularly, to an anti-corrosive flange system for coupling the sanitary cup to the drainage pipe of a bathroom or toilet. B. PRIOR ART DESCRIPTION Flanges are well known for attaching a toilet bowl to a drain tube and the floor of a bathroom. The most common type of flange is that described and illustrated in the expired US Pat. No. 3,846,851 to Pepper, comprising: a section of flat annular flange; a crown section integrated into the flange section; and a tubular skirt section to be attached to the bathroom drain pipe. The typical flange section includes: four circular perforations to attach the flange to the floor of the bathroom, by means of dowels and screws; and two arched grooves that have a wide section to allow the passage of the heads of the screws that will remain in the lower part of the flange section, and a narrow section through which these screws are traversed to retain their head, presenting the string section of the screws upwards to enter the perforations of the foot of the sanitary cup and retain it by means of nuts of the appropriate type. The arched slots with their wide and narrow sections, have as purpose to allow the insertion of the head of the screws once the flange is inserted in the drainage pipe and installed in the bathroom, and adapt the position of the screws to the precise location of the perforations of the foot of the sanitary cup. The crown section has its conical bottom, presenting conicity both in its inner part, so as to be able to receive a rubber packing or similar elastic material in its interior and receive and properly seat the discharge conduit of the sanitary cup, as in its outer part, to bump and supposedly seal the drainage tube. Finally, the skirt section has an appropriate outside diameter, preferably similar to the inner diameter of the drainage tube, to fit snugly on the latter, preferably using an adhesive material to stick and seal together. Mexican Patent No. 160,618 and Utility Model No. 236, describe a flange identical to the expired North American Patent No. 3,846,851 of Pepper, and also illustrated in the North American Patent No. 4,233,697 of Cornwall, published on November 18, 1980 , prior to the legal date of the aforementioned Mexican Patent and Utility Model. Other examples of flanges are claimed in the expired North American patents Nos. 3,181,545; 3,339,215 and 4,090,267. The main disadvantage presented by the flanges described above is that they necessarily have to include the arched grooves with their wide and narrow section to receive and retain the head of the screws with their rope up, to enter the perforations of the foot. of the sanitary cup that is normally rotated to adjust to its correct position and fastened to the screws by means of washers and nuts, for which reason they present the possibility that one of the screws is close to the wide section and leaves position, with the consequent insecurity of subjection of the sanitary cup. All the aforementioned flanges also have the disadvantage that they are designed to use screws, washers and nuts, necessarily metallic, which, when subjected to humid environments and vapors, tend to corrode in the short term. The solution to the problem of corrosion of metal components, would be the use of screws, washers and nuts not metal, but such a solution is not so easy to achieve for these flanges, due to technical problems in the design of the same and poor security of support that they could provide. Regarding its designIn the first place, until now, the design of the flanges has always been conceived to introduce the head of the fastening screws of the flange at the foot of the sanitary cup, so that the string section is upwards to be inserted into the flanges. perforations of the foot of the sanitary cup and hold it by means of nuts. Due to this need, it is difficult to use screws made of plastic material because, due to its flexible nature and its reinforcement needs, the thyme head would have to be manufactured in large dimensions that would make it difficult to pass through the wide and narrow sections . Another technical difficulty in using plastic screws is that it would be very expensive and complicated to make a thread at the edges of the flange grooves, in the plastic injection molds and, for this reason, practically all the designs of flanges illustrated in the aforementioned patents, use the grooves with wide and narrow sections to receive and retain the head of the metallic screws, presenting their rope upwards. In accordance with the anti-corrosive flange system for sanitary cups, of the present invention, the disadvantages of conventional flanges are overcome, since the need for the wide and narrow sections of the slots and the need to use screws, washers and metal nuts to hold the foot of the sanitary cup, because the flange section is simply provided with two or more elongated slots having an appropriate width; at least one provisional metallic screw, like a tap, which is inserted through the perforations of the foot of the sanitary cup and inserted into the slots, in an appropriate position of settlement, to form a thread and which are removed once that the thread was formed; and at least two screws of plastic material with cord similar to the cord made with the screw-tapping so that they can be inserted into the perforations of the foot of the sanitary cup already positioned, with its head on the aforementioned foot, and screwed in Slots of the flange section, serving as a nut for these in any appropriate position. In this way, with the flange in accordance with the system of the present invention, the possibility that it could be misplaced is minimized, as can frequently occur with conventional flanges, and it is also avoided having to turn the cup when installing it. . SUMMARY OF THE INVENTION. It is therefore a principal objective of the present invention to provide an anti-corrosive flange system for sanitary cups that allows the use of screws of plastic material, in normal position, to hermetically couple the sanitary cup to the drainage pipe of a bathroom. or of toilet. It is also a principal object of the present invention to provide an anti-corrosive flange system for sanitary cups, of the nature described above, which is provided with two or more elongated slots having an appropriate width; At least one provisional metallic thyme, like a tap, which is inserted through the perforations of the foot of the sanitary cup and inserted into the slots in an appropriate position of settlement, to form a thread and which are removed once the thread was formed; and at least two screws of plastic material with rope similar to the rope made with the thyme-tapping, so that they can be inserted into the perforations of the foot of the sanitary cup already positioned, with its head on the aforementioned foot, and screwed in Slots of the flange section serving as a nut for these in any appropriate position. These and other objects and advantages of the present invention will become apparent to persons with ordinary knowledge in the field, of the following description of a specific modality thereof. BRIEF DESCRIPTION OF THE DRAWINGS. Figure 1 is a conventional perspective view of a first embodiment of the flange for the anti-corrosive flange system for sanitary cups of the present invention; Figure 2 is a side view of the flange of Figure 1; Figure 3 is a top plan view of the flange of Figure 1; Figure 4 is a conventional exploded perspective view of a second embodiment of the flange of Figure 1, including a plastic lamella for fastening; Figures 5, 6 and 7 are side views of a provisional metallic screw, like a tap, and of the two plastic screws to hold the foot of the sanitary cup to the flange, in accordance with the anti-corrosive flange system for sanitary cups , the present invention; Figures 8 and 9 correspond to a front elevation view of a sanitary cup and its seating in a flange to be held by the anti-corrosive flange system for sanitary cups of the present invention;
Figure 10 is a side elevational view of a sanitary cup seated on the flange, to be fastened by the anti-corrosive flange system for sanitary cups, of the present invention, in its step of forming a thread by means of a metallic screw in a manner of machuelo .; and Figure 11 is a partial view, in section, of the sanitary cup mounted in accordance with the anti-corrosive flange system for sanitary cups, of the present invention. DESCRIPTION OF A PREFERRED MODALITY OF THE INVENTION. The anti-corrosive flange system for sanitary cups, of the present invention, will be described below according to the specific and preferred embodiments thereof, illustrated in the accompanying FIGS. 1 to 11, and comprises: a flange 1 that is constituted by a flat annular flange section 2, which includes a central bore 3 and two arched grooves 4a and 4b for securing the flange to the floor of the bathroom by means of plugs and screws (not shown) and foot 80 of the sanitary cup, to the flange 1 and, if desired, perforations 5, to independently attach the flange 1 to the floor of the bathroom; a set edge 20, normally integrated to the lower surface of the flat annular flange section 2, coincident with the central bore 3 of the flange 1, to settle sealingly on the edge of the drain pipe (not shown) and consisting of a straight lower annular rim, 20 (which could also be conical, as in conventional flanges), having an inner taper 22 in conjunction with the edge of the central bore 3 of the flat annular flange section 2, in order to be able to receive a rubber gasket 30 or similar elastic material in its interior, which in turn receives and properly seats the discharge conduit of the sanitary cup; and a tubular skirt section 40, for coupling to the drainage tube (not shown) of the bathroom, having an appropriate external diameter, preferably similar to the inner diameter of the drainage tube, to fit snugly on the latter, preferably using a adhesive material to stick and seal each other; at least one provisional metallic screw 50, in the manner of a tap, which is introduced, through the perforations 71a and 71b (Figure 8) of the foot 80 of the sanitary cup, into the grooves 4a and 4b of the section of flat annular flange 2, in an appropriate seating position, to form a thread and that is removed once the thread is formed; and at least two plastic screws 60a and 60b with string similar to the rope made with the temporary metal screw 50, so that they can be inserted, through the perforations 71a and 71b of the foot 80 of the sanitary cup, with their head on said foot, and screwed into the slots 4a and 4b of the flange section 1, serving as a nut for these in any appropriate position. In another embodiment of the anticorrosive flange system of the present invention, illustrated in Figure 4, the flat annular flange section 2 can