toilets and limestone after 4 years

The 3 toilets on our Hanse 508 are Jabsco E-toilets (type Deluxe flush) and the valves and tubes looked pretty bad after four years of intensive use although we tried to treat them regularly with different kind of detergents. The biggest work was getting them detached from the walls as they were fixed with thick Sikaflex seals. Of course it would be less worse by flushing them with freshwater (tankwater) but with 3 toilets you would use most of the freshwater just for flushing as we used to empty the blackwater tanks by flushing two or three times. Specially in the Med with high temperatures you can avoid bad smells. Question: Which detergent do you recommend? Jabsco offers this one.