Regardless of your plumbing code, the minimum drain size for a toilet is 3 inches. Water closet's flushing 1.6 gallons (or less) are rated at 3 DFUs (drainage fixture units). Some older model toilets, flushing over 1.6 gallons per flush, are rated at 4 DFUs.
Adhering to the International Plumbing Code (IPC) and Uniform Plumbing Code (UPC), a minimum of 2-inch drainpipe is required for any toilet.
Here are some standard toilet drainpipe sizes and where you'll find them: 3-inch drainpipes: The standard drainpipe used in single-family homes. 4-inch drainpipes: These are used in larger residential buildings (multi-family units with up to 500 fixtures) and high-occupancy spaces (like commercial bathrooms).
Recommended Slope for Toilet Drain Pipes
The universally accepted standard for a toilet drain pipe slope is a quarter inch per foot of pipe (1/4 inch per foot). This means for every foot the pipe travels horizontally, it should drop in elevation by one quarter of an inch to facilitate proper flow.
The typical rule of thumb according to code requires you to run a horizontal pipe for no more than one-third of the total length.
The rough-in distance in the newer homes from the wall to the center of the toilet drain is 12-inch, while, older homes have a distance of anything between 10- or 14 inches. A wall-mounted toilet also needs a 10 inch thick wall to accommodate the flushing system.
But do you know the proper slope? The ideal slope of any drain line is ¼ inch per foot of pipe. In other words, for every foot the pipe travels horizontally, it should be dropping ¼ inch vertically.
Your home's drain lines carry wastewater away from your home and are designed like a tree—the “trunk” is the main sewer line while the “branches” are smaller, secondary drain lines that connect to each water fixture (all secondary lines feed into your main sewer line).
If you've ever wondered what the minimum slope for water drainage is, it is generally accepted that 1/4″ per foot of pipe run is the minimum for proper pitch on a sewer line.
Most modern plumbing codes require P-trap toilets for residential installations.
The trapway outlet on the underside of the toilet sits about 5/8" to 3/4" above the bottom of the foot with a concentric horn that extends down about 1/2". That outlet horn is intended to drop into the opening of the closet flange slightly without touching any part of the flange.
Plumbers for many decades have installed horizontal toilet drain pipes that connect to tee fittings. When you flush the toilet, the water and waste head straight down and immediately hit a 90-degree fitting under the toilet flange.
Slow drainage. Improper venting can hinder the flow of waste and water, causing you difficulties with flushing your toilet. You'll also notice slow drainage in your bathtub or toilet sink, as they typically share the vent stack with the toilet.
In general, the maximum distance of the toilet from the main drain should not exceed 4 meters, with a 2% minimum slope. Within these limits, the plumbing system can guarantee an effective draining, avoiding bad smells and the problem of emptying the siphons.
The “fall” or “drop” should be between 1/40 (1cm down for every 40cm across) and 1/110. Too steep (1/10) then the water runs quicker than the solids so doesn't wash them away (ugh!). Too shallow (1/200) and there won't be enough gradient to get rid of last night's curry.
Main drains are located in the walls and floors of your home, while sewer line drains are located outside underground. Each drain pipe in your home is connected to a different household fixture on one end, including toilets, sinks and bathtubs, and the other end is connected to the main sewer line.
The standard slope is anywhere from ¼ inch to 3 inches per foot depending on the use. An accurate calculation is essential for properly functioning plumbing.
Vertical drops shall be 4 feet (1219 mm) maximum length. Fixture drains that are not increased in size, or have a vertical drop exceeding 4 feet (1219 mm) shall be individually vented.
When connecting a toilet soil pipe, it is advised to never use a pipe smaller than 100mm to carry the waste from said toilets. This size soil pipe is not designed to handle solid waste and can result in a blockage. So 110mm soil pipe is important to consider in this instance.
Toilet discharge hole (vertical): Drain located at floor height; distance is zero. Toilet side-to-side buffer: Measured from the center of the toilet to either side, minimum. clearance is 15 inches to any wall or other fixture; 18 inches is recommended if the bathroom layout allows for this.
Plumbers can install toilets so the tank is snug against a wall, but this requires quite a bit of planning. What's more, if the tank is tight against the wall, the tank lid might not fit well because the lids are larger than the tank and often have an overhanging rear lip. It's easy to keep peace in these situations.
A best practice is to install the toilet flange on top of the finished floor. If you install the toilet flange flush with the finished floor, or even below the finished floor, leak paths will form, because the flange won't be at the correct height to accept the horn at the bottom of the toilet.