I m a certified veterinary technician. Can t answer the question about tank safety, my focus here is for your cats. Be VERY CAREFUL of what you use, many things sold in stores are toxic and/or deadly to cats. I ve seen some horrible results over the years. If you buy a flea product FROM YOUR vet, you will be protecting your cats. The products sold in stores do not work as effectively. Also, you do not need to bathe a cat unless they have a lot of flea dirt (poop) & then use a non soap shampoo. Dawn will strip the oil from their coat & then make your topical flea treatment much less effective. I implore everyone to talk to your vet about flea treatment, trying to go the cheap or neighbor suggested route could end up being lethal to your pets.