Basically I used a 2 part epoxy. I made a little dam at one end and then put in the epoxy. Once it was dry I cut away the dam from the front. I also added some yellow ink (1 drop) to the epoxy to make it look toxic.
The epoxy that I found was for a flower/plant vase. You are supposed to put your fake flowers in a vase and then pour this stuff into it for fake 'forever' water. Maybe you can find some of this stuff.