But Cathay's problems didn't end there. Within ten days, half the toilets on another two flights to Hong Kong became blocked. This time the problems were discovered before take-off, the flights went ahead, but the number of passengers had to be restricted. Airline toilets use high-speed pipes to take waste at up to 110km/h into a holding tank, which is then emptied between flights. Airbus engineers are now fitting new toilet pipes to the airline's fleet, and carrying out deep cleaning. They believe they have solved the problem.