Hossfly,
One rule we CAN pretty much depend on is that lowering a flap will cause a nose down pitching moment on the wing. Oh Yes, that's a given!

What is uncertain is the effect that has on the tailplane. If the aeroplane has NO tail then the effect is nose down. End of.

For aeroplanes with tails then, deflecting a flap down applies that nose down pitch to the wing, and it increases lift.
The effect of a plain flap on a wing is illustrated in Figure 2 below. At all angles of attack the lift coefficient is increased resulting in a greater lift. Notice that when you put the flaps down, the airspeed is initially the same and lift still equals weight, so you are shifting left from the red line to the purple one, not up to it. When the flaps go down, the nose goes down too.
Since weight has not increased the pilot tilts the aircraft nose down a few degrees to get lift equal to weight again. The tail gets tilted LE down as well (since it's connected) which gives a nose up pitch to the aircraft, so we have a bit of nose up, and a bit of nose down.

Added to that, deflecting an inboard flap down distorts the spanwise lift distribution and so the downwash over the tail is altered.
Figure 4 illustrates the view from behind an aircraft, and you can see that the tailplane is flying in the downwash of the wing. As you know, any wing which produces lift must deflect the air downwards behind it. Lift and downwash go hand in hand. The downwash in normal flight has been allowed for when setting the tail angle.
When flaps are used, the tip vortices are reduced and we start a vortex at the outer end of each flap. Next time you fly in an airliner, sit at a window aft of the wing and look out for the flap vortices: they show up well as condensation trails in damp air conditions. The total lift remains the same, equal to weight, so the total downwash is the same, but it is concentrated inboard behind the flaps as illustrated in the lower drawing of Figure 4.

The extra downwash produced by the flaps pushes down on the tailplane, raising the nose, so although the flaps themselves tend to push the nose down (like elevons on a flying wing), this may be partly offset or even overwhelmed by the downwash effect on the tail. It depends on the tail area and position. The smaller the tail area, the less thisnose-up effect & v v..
As illustrated in Figure 5, a small tail well aft of the wing (tail B) or a high-set tail (C) will suffer less downwash than tail A, close to and level with the wing.

So the variables we need to consider are:-<ul>[*]Flap size - chord and spanwise extent[*]flap spanwise position[*]tail area[*]tail moment arm[*]tail height[/list]<br type="_moz" />