The role of aerosols in the epidemiology of disease transmission by toilets has been established.  Specifically, it has been demonstrated experimentally that the flushing action of a contaminated toilet produced a bacterial aerosol comprised of particles of sizes which tend to persist in the air (aerosols) and which are capable of reaching the lower respiratory tract of humans as well as deposit in the nose, mouth and eyes, and which are capable of settling out upon surfaces routinely touched by the hands. 
Other studies have demonstrated that the initial flush of a toilet, the bowl of which had been cleaned and then seeded with an over-night culture of E. coli or E. coli bacteriophage MS-2 eliminated the major portion of the exogenously added organisms, but after subsequent repeated flushes, the number of residual organisms in the bowl, instead of being diminished, often increased.  This increase was found to be due to the adsorption of the organisms to the procelain surfaces of the bowl, with a gradual elution occuring after each flush.  In the case of both bacteria and viruses, the number of organisms in the bowl was found to reach a plateau below which their number could not be reduced by repeated flushing.  It was further found that the flushing of toilets generated droplets (aerosols) which harbored both bacteria and viruses which had been seeded and which remained airborne long enough to settle on surfaces throughout a bathroom.  The number of organisms ejected on flushing was found to be directly proportional to the number present in the bowl water at the time of the flush. 
Periodic cleaning of domestic toilet bowls-- i.e., twice a week or less, is considered inadequate to control microbial contamination of toilet bowls which are used with a higher frequency-- i.e., about four or more times, in the course of a day.  The reason for this is that although stains and microbial activity can be eliminated from a toilet bowl by periodic cleaning, the bowl is recontaminated by subsequent use.  Thus, at best, periodic cleaning of a toilet bowl with a conventional in-bowl cleaning agent provides only temporary control of microbial activity. 
It has been suggested that a potential for disease transmission exists due to the contamination of bathroom surfaces by aerosols generated on flushing of a contaminated toilet.  It is recognized that there is a need for an effective means for providing automatic, reliable and consistent antimicrobial treatment of a toilet bowl. 
Certain non-metered disinfectant dispensing apparatuses produce a build-up of disinfectant actives in the toilet tank over prolonged periods of quiescence, e.g. during vacations.  Such build-up of disinfectants in the tank is wasteful and uneconomical and leads to unnecessarily high concentrations.  The optimum disinfectant concentration is at least about 2 ppm disinfectant in the toilet bowl while unmetered systems may produce concentrations as high as 10 ppm or greater after prolonged quiescence. 
Because of the potential contamination of bowl surfaces and the tendency to form aerosols at the time of flushing, it is desirable that the initial charge of water from the tank into the bowl contain disinfectant.  Since much of the disinfectant found in a bowl, immediately after a flush is completed, comes from the dispenser as distinguished from being stored in the tank, it can be appreciated that the disinfectant concentration in the tank must be maintained at an "effective disinfecting" level even over prolonged periods of non-use.  Failure to do so results in the aerosols formed during the early stage of a flush becoming contaminated rather than being treated with disinfectant. 
The metered disinfecting dispensers described in U.S. Pat.  Nos.  4,171,546; 4,200,606; 4,208,747; and 4,216,027, are designed to overcome the problems associated with long periods of non-use.  These systems generally use an air bubble to isolate the disinfectant in the dispenser from the tank during quiescent periods.  However, this bubble isolation arrangement does not compensate for the disinfectant concentration in the tank being dissipated during such non-use and affords no opportunity for restoring at least, in part, the desired disinfectant activity.  Thus, with these dispensers there is a possibility that the first aerosols generated during the initial flush after prolonged quiescense will not be treated with an effective amount of disinfectant. 
In addition, most devices described to date fail to provide means for responding to various contaminants in the tank and/or the toilet water.  This results in interference with and/or scavenging of the disinfectant by such contaminants.