I've used the "Jacks Magic" stuff that's been around in the pool industry for years. It's great for sticking a large O-ring -- that would otherwise jump out -- in place, say on a Challenger pump. But it's also as I said.

I have used the Rainbow chlorinator silicone, and it's not like that. The Leslie's stuff could be more like the Rainbow stuff, in which case it wouldn't be so good on a Pentair Challenger pump back O-ring . . . but it would be much better everywhere else.