what brand of toilet have you got as some cheap placemaker/bunnings toilets are crap and dont provide a good flush...also if you have poured a bucket of water down your toilet and you say it didnt make any diffrence then you better get a qualified plumber in to have a look at the situation and provide you with some solid answers...on here you will only get theroyitical answers as we need to see the toilet in action to determine what the actual problem is...Good luck.

Ps Dont worry about wasting any money on trying to put CLR down your drain untill you have got a qualified person to determine what the problem is...