Toilet Chemicals Longevity

Hi

Due to the way I use my vehicle I tend not to use the Thetford much. I am also new to the whole experience. 

This means the, currently, the Thetford has been setup but literally not used for a couple of months. 

Do the chemics stay use able on this basis just like if they were in the bottle or should be refreshing on a cycle in case it needs to be used?

 Tried to find an answer but all the answers are assuming it's being used in terms of replacing chemicals.