I keep chickens in an outdoor coop and run in Western New York. In winter, we get temperatures as low as 19º F. in the winter. That leads to the chickens' water freezing. I had a Bucket De-Icer that I had submerged, but the water kept turning rusty, and the element got all corroded. Also, the top of the bucket needed to stay open for the chord, and I prefer to keep the bucket closed so it doesn't get debris inside.
My solution was to make a mini water heater with drinking nipples for the chickens.
I had a 5 Gallon Plastic Hedpack from another project, so I used that. The fact that it is rectangular makes it easier to butt up against the side without it moving around too much. I drilled a 1" hole to insert the Submersible Stainless Steel Heating Element. The threading was 1" NPT, so I had to widen the hole little by little with the dremel, until I could get threads to catch the plastic. I made the mistake (on my first attempt) of drilling the hole too close to a ridge on the container, and the washer wouldn't sit flat, so it would not stay watertight. The second hole shown was just a test hole, since that container was garbage... I ended up using a second container, and it worked fine once I drilled the hole in a flat spot. I just used some teflon plumbers tape on the threads and there are no leaks.
If I were to make another one of these, I would try to install a Bulkhead Fitting so that in the summer, I could remove the heat element and put in a Plug. I feel like the threads on the probe would go in and out easier. The heating element came with a silicon sealing washer which is flexible and waterproof. So far, it's holding well.