It is simply 'graisse de silicone'.
You can get it from model shops (it's used to lube wheel bearings on model cars)
Its only function with an 'O' ring is to prevent it snagging and/or tearing when the joint is tightened. On my filter joints with 'O' rings I only used the slightest smear of silicone. The 'O' ring on the pump filter is fitted with no lube as its removed frequently and is usually wet when being screwed back on.
I guess the issue is why do you feel you need a product like one of these? The answer to that will let you know which one to use. I would not recommend liquid teflon in situatons where joints can be moved or where you may need regular access and thus have to break the seal repeatedly.
Silicone grease is useful to prevent snagging or tearing, though you should also make sure you have no grit or anything else in the seat of the 'O' ring or its opposite face before tightening. Silicon grease will also reduce the deterioration of the rubber over time. You apply it by putting a bit on the ring and spreading it around without leaving any excess.
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