Putting Fabuloso in a toilet tank is not safe for the toilets internal components.
While putting Fabuloso in a toilet tank is safe for you and your family, the Fabuloso when used in a toilet tank can damage the toilets internal components including the rubber and plastic parts like the toilet fill valve and toilet flapper over time.
Fabuloso is a great cleaning product but it also has corrosive chemicals that can break down rubber and plastic parts in the toilet tank and also interfere with the toilet's water displacement and flushing power.
Instead it's best to use products that are designed to be in toilet tanks.
You can however use Fabuloso to clean the toilet bowl itself but it should not be used in the toilet tank.
Fabuloso contains chemicals which can degrade rubber gaskets and plastic parts in the toilet tank and over time the chemicals in Fabuloso can cause the internal components of the toilet tank to break down and cause issues with the toilet.
The damage to the toilet can also cause the flapper to not seal properly and cause a running toilet which can result in higher water bills.
And placing a bottle of Fabuloso in the toilet tank also displaces the water in the toilet tank, which can weaken the flushing power of the toilet and leave remnants in the toilet bowl.