When pushing down on the handle it is very difficult and feels like the seal inside the tank is sticking. How can I fix this?

 

I'd manually open the flush valve and see if you notice anything obstructing it or otherwise making it stick.

 

Often when a flapper get's old and starts degrading it becomes sticky.Check it's condition.Look for ripples in the rubber etc and if the color of it comes off on your hands replace it.

 

I Know Im a bit late with this reply, but I figured I would throw it out there anyway. By any chance, is your toilet a Mansfield, with one their infamous "flush towers" instead of a conventional flapper? If so, then the problem you describe is very common to those type of Mansfield toilets. Kind of like spdavid said, as the seal wears down, it becomes sticky. However on the Mansfield ones, you dont always see ripples or such common signs, when it is breaking down. Anyways, go down to any big box store, and they should have the replacement seal. Remove the flush tower from your toilet, then take off the old seal, and put on the new one. Make sure to slip it into the correct grooves on the base of the tower. Put it back together and re install the tower, and you should be good to go. You may have to flush the toilet a handful of times to get the new seal to be water tight, and not allow any water to leak down into the bowl. Other than that, you should be all set.

 

OMG this is the best. I just logged on to search for this and see others have the same issue (and recently too!). It's amazing how most problems are common problems for others. Anyway, my neighbor told me they have a toilet with a broken handle since they did not replace the seal soon enough (same toilet make). You can be assured I will head to a store to look for a replacement seat and change it before it becomes more involved. I love this site!!!

 

Thanks for the tip. Got a seal ($2.06 with tax) from a big box store and installed it in 5 minutes. Plan on doing other toilets very soon. Seal is about 3" in diameter and red, thanks again!!