Just to add my two cents worth, paint will not adhere to any slick or shiny surface, before you apply the paint be sure you scuff it up so that there is a good surface profile for the coating to adhere to. Glass is probably going to be almost impossible to get paint to stick long term, eventually as it cures it will shrink and become brittle once that happens it will start delaminating from the glass.
As the tank heats up and cools down it will also expand and contract even so slightly that will cause any paint to start delaminating or peeling off.
PVC should be fine as long as you scratch it up real good before you paint it.
The only time paint is going to be harmful is during the cureing process, that is the time when all solvents are escaping from the coating, the solvents will certainly be harmful to your tank. Some alkyds can take several weeks to fully cure, all dependent upon temp and air circulation.
So be careful, with proper surface preparation and curing time it should be fine.
Sorry about being so wordy....Just my professional opinion.