If your toilet tank broke, you need a new tank or maybe even a new toilet, but it might be a few days before you get around to it. During that time, you still need a toilet, and the old one will have to do. All you need to get you through this transition period is a 5-gallon bucket and a source of water. Gravity will take care of the rest.
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Know How a Toilet Works
The procedure for flushing a toilet with a broken tank is fairly simple, but there's a wrong way to do it, so it helps to know how a toilet works to avoid wasting water. When you flush a toilet with a functioning tank, water rushes into the bowl through the siphon jets spaced around the rim and at the bottom. The bowl fills rapidly, and as it does, the water level in the toilet's P-trap also rises until it reaches the top and begins to spill into the waste outlet. As it falls, it creates a suction force that siphons water out of the bowl and takes all the waste with it.
The keyword is "rapidly." If the bowl fills slowly, there won't be enough water in the trap to seal it and create suction, and the only thing that will happen is the water level in the bowl will rise until it's level with the trap outlet. There won't be any siphoning action, so everything that's in the bowl will stay where it is.
Flushing With a Bucket
When it's time to flush the toilet, fill a 5-gallon bucket with water from the sink or shower faucet. Most contemporary toilets will flush with 1 1/2 gallons of water, so you don't have to fill the bucket all the way, but it doesn't hurt to add extra water to ensure a complete flush. If you have to, you can flush with rainwater or water from a nearby stream; it's just going to go down the drain, so there's little danger of contamination.
Once you have water, hold the bucket over the bowl, turn it over and pour out all the contents at once. This is important because if you pour slowly, the flush won't be successful. The water will fill the bowl, but you'll soon hear the familiar gurgling sound of a successful flush as it circles the bottom of the toilet and enters the waste opening. There's no water in the tank to refill the bowl, so it's a good idea to do that yourself to keep the trap full and prevent sewer gases from escaping into the bathroom.
I Don't Have a Bucket
You can flush without a bucket as long as you have some other type of open vessel, such as a pot or saucepan. You'll probably be successful even if it doesn't hold 1 1/2 gallons, but it should hold a gallon at a minimum. You won't be successful if you pour from a vessel that restricts water flow, such as a milk jug or bottle.
A garden hose won't be successful either unless you use a simple trick that requires a bell-shaped toilet plunger, not a dome-shaped sink plunger. Push the end of the plunger into the waste opening to seal it, then fill the bowl until water touches the bottom of the rim. Remove the plunger and let the water flow out. Don't forget to refill the bowl.