A SPARKLING state-of-the-art public toilet block was opened by Hong Kong's very own ''Dr Toilet'' yesterday. Chairman of the Urban Council, Dr Ronald Leung Ding-bong, who earned his nickname by attending an International Toilet Symposium, was at the new toilet block in Chai Wan Park to do the honours. A flushed Dr Leung said: ''This is now one of the best public toilets in Hong Kong and I appeal to the public to keep it that way by using it carefully and considerately.'' The patron saint of public conveniences was also presented with a souvenir plaque, inscribed with the message ''Keep toilets clean, make good use of sanitary facilities'', which will be mounted outside the new block. The ultra-modern block, which took 10 months and $800,000 to complete, includes a baby changing area, a toilet for the disabled and skylights. But the sit-down bowls have been replaced with the traditional squat toilets which Dr Leung says are much easier to clean. The opening ceremony also marked the launch of a mini-drama series on RTHK's Radio 2 which will be part of the Urban Council's health education campaign. It offers advice on food hygiene and will be broadcast every Tuesday at 9.25 am on University of theMorning Suite programme.