When you talk about toilets, water pressure can refer to two different things. It can refer to the flushing technology in toilets that use pressure, instead of gravity, to push the water and waste contents through the bowl drain. It can also mean the pressure of the water that flows from the water supply pipe into the tank.
Toilets that rely on pressurised water to flush the contents look exactly like traditional gravity toilets, on the outside. However, these toilets use a smaller, pressurised tank inside the toilet tank, which stores water and shoots it down through the bowl and into the drainpipe each time the toilet flushes. The smaller tank exerts the pressure of compressed air onto the water to push it out and down, as opposed to gravity toilets which use the force of gravity to pull the water down out of the tank.
Although pressure-assisted toilets are more expensive than their less complicated gravity-fed counterparts, there are a couple of advantages to installing a pressure-assisted model. For one, as the toilet industry as a whole moves towards models that use less water per flush, pressure-assisted toilets can effectively flush out the bowl contents using less water than gravity toilets, because of the extra pressure, or power, of the flushes. This extra power also better pushes the bowl contents out.
The water pressure on a flush toilet also refers to how fast or slow the water flows through the connector that lies between the stop valve and the bottom of the toilet tank's fill valve. If this water flows too fast and hard, it creates an overly noisy tank refill after each flush. If this water flows too slowly, the refill seems to annoyingly last forever, or at least much longer than it should. This pressure can be increased by twisting the stop valve, located about 6 inches above the floor on the toilet's left side, counterclockwise. Decrease the pressure by slightly twisting the stop valve clockwise.
Enough water should flow through the connector tube in about 30 seconds, for you to gauge the water pressure. Check this flow rate by pouring a gallon of water into a bucket and marking the water line on the bucket with a marker or pen. Pour out the water. Twist the stop valve completely clockwise, and disconnect the connector tube from the bottom of the toilet tank, using an adjustable wrench. Hold the end of the connector in the bucket and turn the stop valve counterclockwise, releasing the flow of water into the bucket. Shut it off after 30 seconds. The water level should now be above the marked line. If not, increase the pressure or check the connector for any debris that needs to be flushed out.