If the silicone cement you find is "mildew resistant" then it contains Arsenic and is toxic living things. It says right on the label "not for aquarium use". Silicone cement is for glass. It just doesn't work on plastic. To glue plastic you need the correct solvent that goes with the type of plastic you use. -- Richard J. Sexton richard at aquaria_net Bannockburn, Ontario, Canada +1 (613) 473 1719