Plumbing for a Toilet
Putting in the plumbing for a toilet is actually more work than putting in the fixture itself. There are freshwater pipes that will be under pressure to be connected. There are drainpipes that must also be vented and properly sloped. There are valves and couplings to be concerned about, as well. Most of the time, the average person replacing a toilet will not need to concern him or herself with this. But it is still handy to know about, just in case.
The supply pipe is usually a 1/2-inch pipe that comes up from the floor or out of the wall. There should be a valve on the pipe near where it emerges; to this is attached a flexible hose which will lead to the toilet tank. There are several styles of piping available, plastic and copper are the most common. With plastic pipes glue is used to attach the valve. On copper pipes the valve is generally attached using a nut and a compression ring, but may also be soldered in place. Older lines may be even smaller. The local hardware should have the appropriate valve.
The drain will need to be fairly close to a stack. The stack itself should be at least 4-inches in diameter. A "T" will be required to hook the drain pipe itself into the stack. The toilet drain pipes should be 3 or 4 inches in diameter and slope down toward the stack at a rate of 1/8 to 1/4 inch per foot of length or should be vertical to the ground. From trap to vent on a toilet with a 3-inch pipe should be no longer than six feet, and for a 4-inch pipe the distance is ten feet.
In the case of waste drains carrying fecal matter, bigger, or rather wider, is not necessarily better. It is the flow of water and its level that carries solid waste from the toilet into the drain pipes. If the water can easily flow around the waste, it will not carry it forward. So a 3-inch pipe for a toilet drain is less likely to clog than a 4-inch drain - that is until it reaches the main stack where there are more fixtures attached and wider pipes become more efficient. Much the same reasoning applies to the slope; a gentle slope allows water to build up and push solid waste. A middling slope lets the water run around the waste, possibly allowing it to build up to the point that it will clog.
If possible, the drain pipe should come up through the floor centered as close as possible 12 inches from the wall. This will ensure a good fit and placement of the average toilet. It is best to have the floor beneath the toilet well reinforced. This can be effected by bringing the drain pipe up between joists that are 12 inches on center or adding a bit of cross bracing at the point the pipe comes through the floor and near by. Remember that this is a place where heavy people are likely to be sitting for extended periods of time, and the area may be exposed to occasional water spills or overflows.
To put it simply, the drain pipe (3 or 4 inch) should come up through the floor and be flush with the floor. On top of the drain pipe, the flange is glued. On the bottom it should be connected with a closet bend. The closet bend should be connected by a gently sloping pipe to the stack. Simple, elegant, effective.
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