Why is there a tendency for the nose to pitch-up during a forward slip in a Cessna 172 (According to the TC Flight training manual)?
"If full rudder is used, considerable aileron pressure may be needed to maintain the bank. There will also be a tendency for the nose to pitch up as a result of the banked attitude and rudder input"
It is because of opposite rudder in the bank. In the forward slip and due to angle of bank the rudder input will push the tail down somewhat resulting in the nose coming up as it rotates around the normal axis which is now inclined due to the bank. This is easier to see looking at a model plane.