Crud in toilet

I have a Kohler Toilet that has a "jet" right before the trap way.
There is a buildup of crud that has hardened coming out of this jet and right at the start of the trapway.
I have tried using all kinds of toilet cleaners to remove it and nothing.
Short of using a screwdriver to scrap it, I am hoping someone has had a similar experience and has an idea of how to remedy the situation.

On the lighter side I hope the crud is not brown if your using a screw driver in there.

re: removing crud

(Take this as non-pro advice...)

I would assume the crud you are talking about is just lime minerals or possibly urine salts.

I have had good results with using plain old distilled white vinegar (the kind you buy cheap at the grocery store in gallons) to disolve stuff like this.

I usually turn off the supply water to the toilet and flush once to reduce the water in the bowl, then just pour the vinegar in. The less water in the bowl the higher the acid concentration in the vinegar, the better cleaning.

Then let it sit a good while. if needed a little mechanical cleaning may be helpful (i.e. your screwdriver plan).

Its harmless and cheap to try.

I would clean that out with meuratic acid.........