Walmart, lowes, home depot, it is with the super glues, two part 5min epoxy, clear. Any of those type of two part epoxies are made to bond glass, plastic, acrylic, ceramic, stone, metal, etc. It is permanent so don't get it on any other areas, it won't scrape off without scratching glass. Use masking tape to prevent making a mess if you are worried, just remove the tape before it sets. They also have 1 min epoxy, but you have to work very fast and isn't as strong, if your tank is drained out and you have a clamp, 30 min epoxy is stronger, but if you have to hold the pieces together, use 5 min, it will be plenty strong.