Toilet bowl not filling?

reasons for the low level, has the weather been excessively windy with a low pressure area ? Has anyone been using excessive amounts of paper to cause a plug that would create a larger than normal suction as it travels down the tube ? Is the any cleaning product in the cistern that would prevent the correct amount of water being syphoned out with each flush ? Does the cistern flush c orrectly or maybe thethin plastic sheet needs replacing with age. is there any restriction to the exterior vent pipe to the sewage system?

Maximo
July 2008