The rectum doesn't have enough fluids to have buffer capacity.

The buffer capacity of a strong base is directly proportional to the concentration of hydroyxl ions.

Buffer capacity = 2.303 x [OH-]

Yes. The higher the number of buffers, the higher the buffer capacity.

The buffer maintain the pH constant.

it is defined the capability of a buffer to resist the change of pH.it can be measured quantity that how much extra acid or base , the solution can absorb before the buffer is essentially destroyed. buffer capacity of a buffer solution is determined by the sizes of actual molarities . so , a chemist must decide before making the buffer solution.