Chances are your flapper is leaking and when you go to flush it the first time in awhile there isnt mch water in the tank. So when you flush it a second time you get a better flush. To test try adding food coloring to the tank. If the flapper is leaking then your bowl will slowly turn to the color of the food coloring you added. : We have a toilet that flushes really poorly the first flush (very slow velocity) and well on the second (much higher velocity), even when there is only water in the bowl. Its an older toilet (more than 2 gal/flush). The other toilet in the house(back to back with first toilet with wall between), and all other drains including washer and dishwasher work fine.
