The G-force or centrifugal force is a bit of an illusion, because the only force generated by rotation is the centripetal which draws the pipe and all that's in it towards its centre. However, all things try to stay at rest or move at constant velocity, so what happens is that the centripetal force causes motion in a straight to change to motion in a circle. All objects with mass have inertia, so their inertia says "keep moving" or "keep still", and the centrifugal or G-force is just an object's resistance to moving in a different direction. Anyway, if the pipe is spinning at 300rpm that's 5 revs per second. The centripetal force is mv^2/r, where v is calculated from the circumference of the pipe which is 7(pi). 5 revs per second is a total of 35(pi) inches per second, so v=35(pi)=109.96"/s or 9.163ft/s. The force depends on the mass of the object, so if we go for 5lbs, the force is 5*9.163^2/(3.5/12)=1439.32ft-lbs/s (3.5" is 3.5/12 feet). If the pipe is spinning on a horizontal axis, gravity also acts to reinforce this at the lowest point and counteracts it at the highest point by an amount=5*32ft-lbs/s=160ft-lbs/s. Therefore the G-force is 1439.32/160=9g approx. and the skunk would be subject to between 8g and 10g if the pipe we're spinning horizontally. If it is spinning vertically it will be 9g.
Note that when expressed as a G-force, this value is independent of the mass of an object, because it's a comparison figure with an object's gravitational weight or its mass.