I do not see why you could not. Anything in your dehu, your tank would have already been exposed to. Copper- that is usually what your tap water comes to the faucet in. Faucets typically have brass in them, and it is all put together with tin/ lead/ silver.
Mold is not a factor underwater, and the spores are everywhere- you cannot get away from them. Mold needs certain conditions to multiply, and a food source.
The only thing reason I would not is all the dust, lint, aerosols that have been used in the house will be concentrated in the coil of the dehu. But your tank has already been exposed to it, but not as high a concentration.
The real question is why bother, it is a gallon or 2. Just get it out of the faucet when you need it, and throw the dehu water outside or down the drain.