Hi Billy, we encourage the guys to use them on water tanks but they don't like them because they are difficult to keep in place when working with 2 fixed points, the feedback I have been getting is "the standard hole saw size is a few mill larger/smaller making it very difficult" hence the guys just cut a tight fit onto the water tank and use 202 Silicon around it, I know its not ideal but if Uni seals had some sort of frame on both ends to keep them in place we would have less trouble using them, also great would be a uni seal that has a bit of flex making the insert easy and at the same time creating a seal.. To much to ask for? lol