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How a Toilet Tank Works

Learn how a toilet tank works from Master Plumber John Wood in this plumbing repair video from Howcast.


Okay, so today I'm going to try to talk a little bit about how a toilet tank works. A lot of people are completely mystified as to the very simple machinations of the toilet tank. You can save yourself a lot of money trying to tackle some of these very simple repairs yourself, with a few exceptions when you're talking about pressurized toilet tanks or maybe a flushometer tank inside the wall. Leave that to a professional.

Generally speaking, a toilet you would get and assemble in two pieces, with a water control valve, a seal, and something to flush it, they operate on a very simple principle. When you approach a toilet and the tank is filled with water and it's sitting idle, the way that toilet flushes is via gravity. A couple things happen: you press the tank lever, and a seal of some sort, which I'm going to show you in a moment, opens up inside that tank, water rushes from the tank into the bowl, flushes the contents of the bowl, and then the tank fills back up again, endlessly. Okay?

I've got my little sketch here, forgive my drawing skills. This is a toilet, at the face, when you're walking in and looking at it. Here's my tank lever up here, usually on your left on the top left. This is the bowl, with water in it. You'll notice this little stop right there, I put an X. On blueprints, stops and valves are drawn with an X because it cuts the water off. A little warning: a lot of times when these little valves have been living under your toilet for a long time and nobody's touched them for 20 years, the moment you touch them, water will start shooting from the handle. It's always a good idea when tackling a water-piping repair, or repair where you're dealing with water under pressure from the street, know where the shut-off valve is before that. In case this snaps off or something horrible happens, you can run downstairs to your basement and just shut the main off and triage the situation until a professional gets there and takes care of it. But let's not talk about that, let's talk about this valve working just fine.

A couple of issues happen when we have problems with toilets, most commonly running, and you have the toilet tank sweating. That's because you have a warm environment, or comparably warm environment, with cold water rushing through it. What happens is, water comes up from this supply pipe into the toilet and fills this tank. That ball, everyone's seen this ball, OK? It rises up on the water and simultaneously pushes down a washer sitting inside of this valve head. That washer pushes down and shuts off the supply coming in. That's how this works. When you flush the toilet and this seal comes up, I'm going to draw that in there. There are two positions: that's the flapper, the seal sitting in the closed position, holding water in that tank. The up position, it just kind of gets snapped up like so, and lets all that water rush down. Then this ball drops, lifting the washer away, like so. Water rushes in, it fills, and the tank rises once again, and the ball pushes it down and off again.

Let's say a big service call for me is a sweaty toilet tank and a hissing sound. That's because one of two things, or two things, is happening. This washer inside this valvehead has failed, in which case you need to replace this valve. This old-fashioned one here, made out of brass, is inferior, believe it or not, to the plastic jobs out there today. This is called a ballcock, cock being a valve, this being the ball that operates it. These are replaced, generally speaking today, with what we call a fluidmaster. It's a black and grey valve, you may have seen it, they cost about nine dollars at the home centers,and they just quickly swap out.

If this valve, the washer inside this valve has failed, it's going to fail to stop the street pressure water from coming in all the time, so it's just going to overfill. If the tank overfills, what happens? It rises, rises, rises, and eventually goes over this overflow tube right here on the Douglas valve, this assembly is called the Douglas valve. The reason that overflow tube is there is so that if this fails, we don't fill out the tank, onto the floor, endlessly and flood out the whole house. So that's a safety, there.

The other reason that the tank would be sweating is again, there is water constantly moving in that tank, causing condensation, is if this flapper failed. If the seal failed, and there are a variety of seals but I'm just showing you this for the sake of illustrating a point. If this seal has failed, the water is going to continuously run down into the bowl. You'll see it trickling into the bowl, you'll see the little rivulets of water in the bowl. It's very common again, so you'll replace this seal. It can be done very simply. You don't even have to shut the water off to replace this seal actually, it'll just keep rushing into the bowl. You kind of pop it off these two little ears right here on the side of the Douglas valve, and that rubber seal just kind of snaps on. You put the new one on, and you attach the chain to the tank lever.

When you call a plumber into your home, you want them to change all of it in one shot, OK? Don't let contractors nickle and dime you or try to take the easy way out. Chances are, if the flapper has failed, so has this. Conversely, if the valve has failed, so has the flapper. Make sure everything's right. We want no jiggly handles, jiggly handles are a no-no in the trade. If things look rusty, replace them.

One problem: a lot of times when people think they're going to get off the hook easily with a basic toilet repair, is that I go there, and because the age of the toilet, let's say 20 years, there are two bolts inside the tank. If you were to look down into the tank from a bird's-eye view, there are two brass bolts sitting roughly here and here, down at the bottom of the toilet tank. Those bolts are very simple, they're just long brass bolts with a rubber washer underneath them. When the toilet's originally installed, they go down through the bowl and then you attach nuts from below. It connects the tank rigidly to the toilet bowl. What you see a lot, or what I see a lot is, I'll put my hand on the tank and the tank wobbles back and forth. Now you need a new toilet because it's not worth the labor and the work to cut these out. You can get a decent toilet for around $150. Most bolt jobs like that are a pain. You have to get a power saw and cut it off. Now if the toilet's a $2000 toilet, sure, we'll do it and we'll rebuild it, but very, very rarely will I do that. Be aware of that.

You can also tell by reaching down into the tank and touching the rubber with your finger. If a black patina comes off on your finger, that's the rubber wearing out. There's nothing gross inside here, this is all actually clean water. It's the bowl that you don't want to be putting your hands in, not without gloves anyway. So do an evaluation of your toilet before you put any money into fixing it with a plumber. Most of the time it's better to just replace the toilet outright, especially if it's been in there for 15-20 years.

If you're going to tackle doing this job yourself, and it's a very simple job to do, remember we're going to shut that valve off. Your most common culprits to get your toilet back up and running without reinventing the wheel here on it is the water control valve, which will be between $9-$12, the flapper or the seal which could be upwards of $20-$25, and then the tank lever. The tank lever is just a few dollars for the cheap ones, but you can get up into the $30, $40, or $50 range if you're getting a chrome lever.

Generally speaking, if you're handy and you're not intimidated by this stuff, you can fix your toilet for about $50.

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