Toilet Types – One Piece or Two Piece

All modern toilets either have their tank and bowl molded together as a single assembly (one piece toilet) or have a separate tank and bowl held together by long bolts (two piece toilet).  The flush valves for one piece toilet types mount inside the tank using a “T-flange” which fits down inside and below the drain hole to pull the valve gasket tight against the lower floor of the tank.  These toilets are generally easier to work with for that reason but can have smaller tanks and can be more difficult to fit.

The flush valves for two piece toilet types use a large nut that tightens down on the outer tank bottom to fasten the valve.   Installing a two piece valve requires that the tank be fully removed and then reinstalled.  This assembly process is more work, but the tank is usually larger and easier to fit with more room for the fill and flush valves.

See our “Help Me Choose” button over to the right for pictures and a guide to determining your toilet type . . .

General Sizing

Most common standard toilets are generally considered to be either “2-inch or 3-inch” by naming convention. This refers to the INSIDE pipe diameter within the toilet and down through the floor drain. There are also some in between and larger size toilets, but these are considered non-standard and require adapters (see next paragraph below) or fittings from the original manufacturer because no standard flush valves of any type will fit, whether they are standard flapper or dual flush piston valves.

Since the toilet size refers to the inside pipe diameter, this means the drain hole cut-out inside the tank will naturally be larger. How much larger depends on the initial hole cut-out and the after-cure tolerance of the ceramic or plastic composite during manufacturing.

Flush Valve Drain Hole Sizing

In most cases for 2-inch toilets, this will result in a drain hole size in the range of 2 3/8″ to 2 3/4″ and so the flange and gasket combinations on our 2″ dual-flush valves will fit and seal this size range effectively. Any drain hole size larger than 2 3/4″ does not allow enough gasket overlap and may result in leaking.  To solve this potential problem with larger drain hole sizes, we offer an optional shim washer set that fits onto the flush valve and provides the additional overlap required to cover and seal the larger tank drain, see part number WSHR2-2ST1.

Similarly for 3-inch toilets, the drain hole should fall in the range of 3 3/16″ to 3 3/4″ and so the flange and gasket combination on our 3″ dual-flush valves will fit and seal that range.  Any drain holes size larger than 3 3/4″ does not allow enough gasket overlap and may result in leaking.  But we also offer an optional shim washer set for this sizing problem as well, see part number WSHR3-2ST1.

Note that in most cases, the toilet size can be determined by measuring the lip of the flapper valve base. If the flapper lip is roughly 1 7/8″ to 2 3/8″ in diameter, that indicates a 2-inch toilet. If it is more in the 3″ range, that is most likely a 3-inch toilet. See our illustration of measuring the flapper valve base lip over on the Products > Help Me Choose tab.

In other cases where the flapper base is an odd design or the valve is not a flapper type, the tank and valve will need to be removed to allow direct measurement of the tank drain hole.

Flush Valve Height and Tank Sizing
The inside height of most standard toilet tanks as measured from the bottom of the tank to the inside top of the lid is around 12″.  When mounted, our 2″ flush valves are 8″ high, but require 10″ of height overall for proper clearance of the flush cable.   Similarly our 3″ flush valves are 9″ high, but require 11″ of height for the cable clearance.

There also needs to be enough width and depth inside the tank to allow for the other components to all mount and fit together without interference.  In most cases, this is not a problem, but in smaller tanks, it make take some trial and error in rotating or otherwise repositioning the various components to get everything inside.

For toilets with low profile or otherwise very small tanks, it is best to stick with the original factory components because it is unlikely than any of the standard retrofit kits will fit.

Filler Valve Inlet Hole Sizing

The filler valve inlet hole in the tank is much easier to fit because it is almost always 1″ or slightly larger and fits standard 15/16″ threaded filler valves. Most filler valves, including our models, will fit and seal a hole size in the range of 1″ to 1 3/8″.

Flush Handle or Push Button Actuators Mount Hole Sizing

The flush actuator mount hole can be a little tricky sometimes because there are two commons sizes, 5/8″ and 3/4″ square, which will also vary a little due to the same manufacturing tolerances. Most flush actuators, whether lever handle or push button, will have a removable rubber collar that will accommodate both sizes. All of our kits have this collar arrangement unless otherwise specified. In extreme cases where the hole is a little smaller than 5/8″, the plastic shoulder of the flush mechanism may need to be sanded or filed slightly. Then on the other extreme, where the hole is slightly larger than 3/4″, the rubber collar may need to be shimmed with tape or other suitable material to enlarge it further for a tight fit.

Still other flush actuator mount holes are round or odd-sized, again intended for a specific manufacturer actuator.

Anytime a non-standard smaller hole size is encountered, there is always the option of enlarging it with a ceramic file or grinder. This may sound like a lot of work, but in most cases, the hole only needs to be enlarged slightly and the ceramic or plastic composite usually cuts away fairly quickly and easily. Then upon completion, the resulting fitting hole is now at a standard size and can accept any number of standard fittings on the market.