Flange height, wax ring selection, bolt tightening sequence, and water supply connection
Toilet installation is one of the most common DIY plumbing projects. While conceptually straightforward, proper installation requires attention to detail at several critical points: correct flange height, appropriate wax ring selection, proper bolt tightening sequence to prevent cracking, and leak-free water supply connection.
Modern toilets come in two main configurations: two-piece (separate tank and bowl) and one-piece (integrated tank and bowl). Two-piece toilets are lighter, easier to handle, and more common for DIY installation. The installation process is similar for both types, with two-piece requiring an additional tank-to-bowl assembly step.
The toilet flange (also called a closet flange) is the fitting that connects the toilet to the drain pipe. Correct flange height is critical for creating a proper seal with the wax ring.
Ideal Position: Flange top surface should be 1/4" ABOVE the finished floor
Acceptable Range: Flush with floor to 1/4" above
Problem Range: More than 1/4" above or any amount below floor level
| Problem | Consequences | Solution |
|---|---|---|
| Flange below floor level | Wax ring can't seal properly, leaks likely | Use flange extender/spacer ring to raise flange |
| Flange 1/2" or more above floor | Gap too large for wax ring, unstable toilet | Stack two wax rings or use extra-thick wax ring |
| Broken or damaged flange | Can't secure closet bolts, toilet rocks | Install repair ring/flange over existing flange |
| Flange rotated wrong direction | Closet bolt slots in wrong position | Remove and reinstall flange in correct orientation |
| No flange present | Can't mount toilet properly | Install appropriate flange for pipe type (PVC, cast iron, etc.) |
The seal between the toilet and flange is critical for preventing sewer gas and water leaks. Two main options exist: traditional wax rings and modern wax-free gaskets.
| Type | Best Use | Pros | Cons |
|---|---|---|---|
| Standard Wax Ring | Most installations, flange flush to 1/4" above floor | Time-tested, inexpensive ($3-5), moldable, forgiving | One-time use, messy, temperature sensitive |
| Wax Ring with Funnel | Flange slightly below floor, extra security | Plastic funnel guides waste into pipe, extra seal | Slightly bulkier, costs more ($5-8) |
| Extra-Thick Wax Ring | Flange up to 1/2" above floor | Fills larger gap, same benefits as standard | More expensive ($8-12), may be too thick for some situations |
| Stacked Wax Rings | Flange 1/2"+ above floor (not ideal) | Works when gap is too large, uses standard rings | Less reliable than single appropriate ring, very messy |
| Wax-Free Gasket | All installations, especially if toilet may be removed | Reusable, clean, consistent seal, no temperature issues | More expensive ($15-25), less forgiving of uneven flanges |
Closet bolts (also called toilet bolts or T-bolts) secure the toilet to the flange. Proper bolt positioning and installation prevents toilet rocking and ensures even pressure on the wax ring seal.
| Specification | Standard | Notes |
|---|---|---|
| Bolt size | 1/4" × 2-1/4" or 1/4" × 3-1/4" | Longer bolts for thicker wax rings or extenders |
| Spacing (center to center) | 12" (standard rough-in) | 10" and 14" rough-ins also exist but less common |
| Positioning | Perpendicular to wall | Bolts should align left-right, not front-back |
| Material | Brass or stainless steel | Avoid zinc-plated - corrodes in bathroom environment |
Over-tightening toilet bolts is the number one cause of cracked toilet bases. Porcelain and vitreous china are brittle materials that crack under uneven stress. The correct technique involves gradual, even tightening while checking for level and rock.
Lower toilet straight down, aligning holes with closet bolts. Do not rock or twist.
Apply even pressure to compress wax ring. Rock gently to seat toilet evenly.
Use plastic washers between nut and porcelain to distribute pressure.
Tighten by hand until snug but not tight.
Use wrench to tighten one bolt 1/4 turn, then the other bolt 1/4 turn. Repeat.
Push on toilet from different angles. If it rocks, continue tightening gradually.
Toilet should not rock. Nuts should be snug but not extremely tight.
Wax compresses over time. Check again after use and tighten slightly if needed.
If toilet continues to rock even with tightened bolts:
The water supply connection brings fresh water from the shutoff valve to the toilet tank. Proper connection prevents leaks and ensures adequate water flow for flushing.
| Type | Material | Pros | Cons |
|---|---|---|---|
| Braided Stainless Steel | Flexible hose with SS braid | Most reliable, easy to install, various lengths | Most expensive ($8-15) |
| Braided Polymer | Flexible hose with polymer braid | Affordable ($4-8), flexible, corrosion-resistant | Shorter lifespan than SS (5-7 years) |
| Chrome-Plated Copper | Rigid copper tube | Clean appearance, durable | Must be bent to fit, harder to install, can kink |
| Plastic/Vinyl | Flexible plastic tube | Cheapest ($2-4) | Not code-compliant in many areas, prone to failure |
| Component | Standard Size | Notes |
|---|---|---|
| Shutoff valve outlet | 3/8" compression or 1/2" compression | 3/8" most common for toilets |
| Toilet fill valve inlet | 7/8" slip joint nut (3/8" thread) | Universal size for most toilets |
| Supply line length | 12", 16", 20", 24" | Measure from shutoff valve to fill valve inlet + 2" |
| Thread type | Valve end: compression; Tank end: slip joint | No thread tape needed - uses rubber washers |
Two-piece toilets require assembly of the tank to the bowl before installation. This connection must be watertight and properly tightened to prevent leaks and wobbling.
Place large rubber gasket over flush valve outlet on bottom of tank. Some gaskets are adhesive-backed.
Usually 2 or 3 bolts. Place rubber washers inside tank on each bolt.
Align bolt holes in tank with holes in bowl. Gasket should seat in bowl's tank mounting surface.
Metal washer then nut on each bolt. Use brass or stainless hardware.
Get all nuts finger-tight before using wrench.
Tighten each bolt 1/4 turn, alternating between bolts to keep tank level.
Tank should be level and centered on bowl, parallel to wall.
Tank should not rock. Don't crack the porcelain - moderate tightness is sufficient.
| Leak Location | Symptoms | Solution |
|---|---|---|
| Base (wax ring) | Water around base after flushing, sewer smell | Remove toilet, install new wax ring, reset toilet |
| Tank-to-bowl gasket | Water dripping from between tank and bowl | Tighten tank bolts slightly or replace gasket |
| Tank bolts | Dripping from bolt locations under tank | Tighten bolt, replace rubber washers if needed |
| Supply line connections | Dripping from valve or tank connection | Tighten compression nut 1/4 turn at a time |
| Fill valve seal | Constant water in tank, hissing sound, water bill increase | Replace fill valve or just the seal assembly |
| Flush valve seal (flapper) | Water running into bowl, tank refills periodically | Replace flapper valve |
| Condensation | Water on outside of tank (not a leak) | Normal in humid conditions, improve ventilation or insulate tank |
Note: Some jurisdictions require licensed plumbers for toilet installation. Check local codes and requirements. Water supply lines should be replaced every time a toilet is replaced. Wax rings are single-use only.
Disclaimer: This guide provides general information about toilet installation. Always follow manufacturer instructions for your specific toilet model. Local plumbing codes vary - check with your building department. Some jurisdictions require licensed plumbers for toilet installation. Replace wax rings and supply lines with every toilet replacement.