Aquarium Sealant's

[shoddy mac]

does anyone know where I could get a sealant for creating a larger sized tank the glass that is 5/8" thick and 3' sheets. any help would be helpful

 

[03]

for building a new fish tank i guess?
you can buy silicone calking gun size tubes at your local fish store some of them will carry them,have you built a tank before?????????