The bottles are either polypropylene or polyethylene...same stuff that Elmer's glue/wood glue bottles are made out of. It's very difficult to adhere much of anything to either of those materials.
You can attempt to remelt the plastic to seal the leak with a soldering iron etc, but that usually ends in failure unless you have experience. Here are a few videos about how to repair them:
The Ronco tank video is a good one; they are repairing by spin welding using a router motor. These folks make loads of RV tanks.