All toilets are NOT made the same. Some brands tend to have more problems than others. The low volume toilets now required do give some problems, especially if they are early models. Later ones seem to have gotten some of the problems fixed. What brand is yours and how old is it?

I'm not sure what brand. The house is about 40 years old and I think it is the original toilet.

I had a similar problem with a 15 year old toilet in my 50 year old house.

After first checking the main plumbing stack for an obstruction I found the cause of the problem. I had lifted the toilet off the floor and noticed that the cast iron drain pipe connected to the toilet flange had a "sludgy" deposit on the inside of the pipe. The deposit had effectively reduced the 3" diameter pipe to a 1" diamter.

I hired a plumber who used a power auger to clean the main stack and drain right out to the sewer. That was about three months ago and I haven't had another problem since.

I was in the middle of eating my dinner of roast pork, potatoes, veggies and THICK brown gravy, when I opened up this post....yeeeeeeech.
Thanks fella's, I really needed to read about thick slimy sludge residue & stuff.
I'll remember to check out other posts while I'm eating :O(

Glad you got it cleared.

Brian.