Maybe you shouldn't
Not all pills can safely be crushed without affecting the bioavailability of the medicine within.
Assuming the pill in question is crushable, it may clog the peg (g-tube) unless the pill dissolves in its entirety. To accomodate peg's, many drug manufacturers make liquid versions of pill-medicine. Alternatively, your pharmacist may be able to compound the pill into a liquid, or substitution made.