Dump water operation and advices.
Important to read.

In the aircraft.cfg file have been added appropriate-sized auxiliary (drop) fuel tanks  
to represent the fire retardant payload.
Because of this IT IS VERY IMPORTANT to remember to adjust the total fuel load to keep it below the MTOW for land or water takeoffs. These are given in the Performance section of the ircraft.cfg file. Not correcting those values would be difficult to take off from the runway with the overveight and impossible to take off or even move when floating in the water. 
Using of drop tanks to simulate the water tank weight give realistic feeling of weight decrease when the water/fire retardant is dropped. 
It seems that there is not a valid solution to restore the weight of water/fire retardant in the tanks, or we have not found one. The only valid solution is to select a different aircraft and the select again the CL215.

However It is possible to simulate water tank refill and drop using the water dump panel and perform water dumping operation with water dropping effect, but you cannot feel the effect  of weight decrease when the water/fire retardant is dropped if you don't use the right weight in the auxiliary water tanks. This is only possible when you load initially aircraft and adjust the auxiliary fuel tanks with the appropriate quantity that should be maintained below the MTOW, Max Take OFF Weight.





