so I've noticed a tiny bit of, what seems like, some dark grit, on the very bottom of my fuel gerry can.

Often I bring fuel to the car when it's stored off the road.

Is it advisable to ever put pressurized water in such a jerry can to attampt to dislodge such grit or is that a big no no.

I've never put water in a gerry can and something tells me not to even though it would dry out. I don't even know if that would remove the grit.