yes its safe, i would rinse after doing it tho.
also, make sure it has a good way to bond, i have used this several times to make "quick" structures with assorted pvc and have found that it might fail over time. the larger one i made didn't but the smaller one did. of course pvc isn't the best surface for most glues to bond to, tho............ maybe if you roughed the surface slightly with something abrasive like sandpaper.....
in my case they were pieces i might use around the house and i needed caves "right then" so i wasn't concerned with being able to remove the glue later and actually it was sort of a plus.