Fixing a weak flushing toilet requires you to first determine the cause of the weak flushing problem. If you have a first generation low-flush toilet, though, the toilet will not flush as well as other toilets. By checking the inside of the tank, where the manufactured date is displayed, you can tell your toilet is a first generation low flow if it was made between 1994 and partway through 1997.
Test for Clogs
Your toilet's weak flushing power may be the result of a partial clog in the toilet's drain line. Partial clogs will still let water and waste flow down the drain line but at a decreased amount, which will result in poorer flushing power. By pouring a bucket of water quickly into the toilet's bowl without spilling the water, you can observe if the toilet flushes or not. If the toilet flushes. it does not have a clog; if it still struggles, it has a partial clog.
Partial clogs in the toilet's drain line can eventually turn into a complete blockage of the drain line, meaning the toilet will not flush at all. Removing a partial clog does not present as much of a challenge as removing complete blockages. Use a plunger on the toilet first, but use a funnel-cup plunger if possible since they work better on toilets. A funnel cup plunger has a rounded bottom, making it sit down in the toilet's drain better. After you pump the plunger's handle up and down at least a dozen times, if you see no improvement with the clog, use an auger. Feed the auger's flexible line down the toilet's drainpipe as you spin it clockwise. Spin the auger counterclockwise as you pull it out of the toilet.
If the toilet flushes fine with the bucket, hard water deposits have clogged the small port holes that sit below the rim of the toilet. When you flush the toilet, the water that drains out of the tank enters the bowl through the ports. Clean out the port openings with a sharp and narrow object such as a stick. You can use a wire hanger, but you need to be cautious or the metal hanger will scratch the porcelain. After you have cleared out the port openings, flush the toilet to see if you need to perform further cleaning.
If the toilet still does not flush well, you will need to clean the port passageways inside the toilet's bowl using muriatic acid. You need to ventilate the bathroom as well as possible while using the muriatic acid, and wear a ventilator to avoid inhaling the acid. Mix 1 part muriatic acid with 10 parts water in a bucket, and pour half of the bucket slowly down the overflow tube in the toilet's tank. Wait 30 minutes for the acid to break apart the hard water deposits inside the bowl, and flush the toilet. Pour the other half of the bucket down the overflow tube, and wait another 30 minutes before flushing the toilet again.