Well now you won't get far with a knitting needle. You may have a slight blockage the other side of the water trap bend which you obviously can't see. Get some one to fush the toilet while you are looking in the manhole it feed into and note the speed of flow. Then do same with outher toilet check it's flow. If there is a noticalble difference then the slight blockage could be the problem. Plung the toilet, with water in it of corse, using the cup type drain plungers as rods won't go around the bend. A mix of boiling water and causitc soda can some times clear a blockage. Wear rubber gloves as caustic soda burns skin when wet. I've used both methods to clear minor blockages in mine.
Bob
September 2009