Will a bidet fit my toilet? The five checks to run before buying an attachment or an electric seat
Bolt spread 5.5 in, round or elongated bowl, a reachable fill valve for the 7/8 in T-valve, a flexible supply hose, and a GFCI outlet within a 3.9 to 4 ft cord.
- Verified
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- 8 min read
- 5 sources
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Short answer
A bidet attachment or electric bidet seat fits a standard two-piece toilet when five things check out. The seat bolt spread: Brondell’s Swash DS725 manual says the seat installs only on toilets with a 5.5 inch (14 cm) spread. The bowl shape: Brondell’s elongated DS725 is 20.87 inches long and the round one 19.5, so the seat is ordered to the bowl. A reachable fill valve under the tank: the LUXE Neo 120 and BioBidet SlimGlow manuals both install their T-adapter at the tank fill valve, not at the wall shut-off. A flexible supply hose with a 7/8 inch ballcock nut at the tank end. And for an electric seat, a grounded GFCI outlet within the cord: 3.9 feet on the TOTO Washlet SW3024, 4 feet on the BioBidet Bliss BB-2000. A one-piece or skirted toilet that hides the fill valve fails the third check and needs the maker’s alternate T-valve. Measure the bolt spread before buying anything.
The picks
The fill valve nut under the tank is reachable and the supply hose is flexible
LUXE Bidet 7/8 x 7/8 x 1/2 inch Cold Water T-Adapter
7/8 x 7/8 x 1/2 inch T-adapter, the size the LUXE Neo 120 manual prints for its fill valve connection; cold water only
A two-piece toilet with a reachable fill valve and no outlet nearby
LUXE Bidet NEO 120 Bidet Attachment, White
Non-electric cold water attachment; the manual installs its T-adapter at the tank fill valve and warns of a seat gap above 1 inch with curved-lip seats
If your toilet is a one-piece skirted model, read the second table before anything else: the cheap T-adapter every attachment ships with only fits a fill valve you can reach.
Which checks decide it?
Every figure in this table is one manual’s printed number for one model. Other seats from the same maker may differ, so the manual for the seat you order is the last word.
| Check | What passes | Who says so |
|---|---|---|
| Seat bolt spread | 5.5 inches (14 cm) between the two bolt holes at the back of the bowl | Brondell Swash DS725 manual: the seat can only be installed on toilets with that spread |
| Bowl shape | Round or elongated, and the seat ordered in that size | Brondell DS725: elongated 20.87 in long, round 19.5 in, both 15.5 in wide. BioBidet Bliss BB-2000: elongated 20.9 in, round 18.9 in |
| Fill valve access | You can see and turn the nut under the tank where the supply hose meets the fill valve | LUXE Neo 120 and BioBidet SlimGlow manuals: the T-adapter installs there, not at the wall |
| Supply hose | A flexible hose, not rigid pipe | LUXE Neo 120 and Brondell DS725 manuals: replace a rigid line with a flexible hose |
| Seat gap (attachments) | Under 1 inch between seat and bowl once the attachment is in | LUXE Neo 120 manual: under 1 inch is closed with seat bumpers, over 1 inch may need a different seat |
| Outlet (electric seats) | A grounded GFCI outlet within the cord length | Brondell DS725 and BioBidet Bliss BB-2000 manuals |
The bolt spread is the distance between the centres of the two seat bolt holes. Bowl length is measured from those bolt holes to the front rim; how to take it is the job of the toilet seat size page.
The seat lengths above are the bidet seat’s own dimensions, not the bowl’s. A round bidet seat on an elongated bowl leaves bare porcelain in front; an elongated seat on a round bowl overhangs it.
Two clearance points come from the LUXE Neo 120 manual’s troubleshooting section. A nozzle that sticks can be too close to the toilet tank, and the fix is to move the attachment forward. If the seat bolts are too short once the attachment plate is under the seat, fit longer bolts from the seat maker.
What changes on a one-piece or skirted toilet?
Brondell’s DS725 manual puts it plainly: many modern toilets have sleek designs intended to cover and camouflage plumbing connections, which makes a standard Swash installation difficult or impossible. The fill valve is still there. You just cannot get a wrench on it.
| Toilet | What it hides | What the makers offer |
|---|---|---|
| Two-piece, exposed tank bottom | Nothing | The standard T-valve in the box, at the fill valve |
| One-piece or skirted, fill valve concealed | The fill valve nut | Brondell: its Alternate Swash Bidet Seat T-Valve. LUXE and BioBidet manuals: no alternate part named |
| Bolt holes reachable only from the top | The nuts under the bowl rim | Brondell: the Top-Mount Brackets included with the DS725 |
| Toilet with a built-in seat or washlet | The seat bolt holes | Not covered by any manual read for this page: ask the toilet maker |
The honest limit of this page: the LUXE, BioBidet and TOTO manuals read here all require fill valve access and describe no other route. Retailers sell a tee for the 3/8 inch compression thread at the wall shut-off, but no maker document read for this page supports it, so it is not recommended here. If the fill valve is concealed, ask the maker before ordering.
How does the water connection work?
The T-valve is a tee fitting placed between the toilet tank’s fill valve shank and the supply hose. Every manual read here puts it at the tank. The LUXE Neo 120 manual says the T-adapter installs at the fill valve, not at the cold water supply valve coming from the wall, and Brondell’s DS725 manual says its T-valve connects to the fill valve directly under the tank and does not connect at the wall.
| Part | Size as printed | Manual |
|---|---|---|
| T-adapter | 7/8 x 7/8 x 1/2 inch | LUXE Neo 120 |
| T-valve | 7/8 x 7/8 x 3/8 inch | BioBidet SlimGlow |
| Bidet hose | 1/2 x 1/4 inch | LUXE Neo 120 |
| Replacement supply hose | 7/8 inch ballcock at the tank, 3/8 or 1/2 inch at the wall valve | LUXE Neo 120, BioBidet SlimGlow |
| Supply pressure | 20 to 80 psi (SlimGlow); 14.2 to 106.6 psi (Brondell DS725) | BioBidet SlimGlow, Brondell DS725 |
The 7/8 inch ballcock thread is the tank end of a standard toilet supply hose, the same nut you would undo to change the fill valve on the toilet fill valve by model page. If the existing line is rigid pipe, the LUXE manual says to replace it with a flexible hose whose top connection is 7/8 inch ballcock and whose bottom is 3/8 or 1/2 inch to match the wall valve.
The LUXE 7/8 x 7/8 x 1/2 inch T-adapter is the size the Neo 120 manual prints, sold on its own for a replacement or a metal upgrade. It is cold water only, and it fits nothing you cannot reach.
Both attachments whose manuals were read here are cold water units: the Neo 120 is described as a cold water, non-electric unit, and the SlimGlow specifies a cold water source. No maker page read for this article offered a warm line, so this page does not describe one.
What does an electric seat need that an attachment does not?
An electric seat adds a power cord, so the outlet decides the fit as much as the bowl does.
| Seat | Power | Cord length | Outlet requirement as printed |
|---|---|---|---|
| Brondell Swash DS725 | 120 V, 60 Hz, 660 W | Not printed in the manual | Only a grounded GFCI outlet and a grounded three-prong cord |
| BioBidet Bliss BB-2000 | 120 V | 4 ft | Grounded 120 V GFCI outlet; an extension cord, if needed, three-prong on a GFCI outlet and rated at least 10 A |
| TOTO Washlet SW3024/SW3074 | AC 120 V, 60 Hz | 3.9 ft (1.2 m) | Grounded cord and plug; the warranty section mentions a 120 V, 60 Hz GFI socket, but no install-step GFCI line |
All three manuals say to check with a qualified electrician if the grounding instructions are not understood. An outlet that is missing, ungrounded or beyond the cord is a job for a licensed electrician, and whether GFCI protection is required there is set by the electrical code as adopted where you live, which varies. Two TOTO manuals that reportedly print a GFCI requirement returned HTTP 403, so no GFCI figure is attributed to TOTO here.
Before you buy anything
Put a tape measure on the two seat bolt holes and a hand under the tank. If the spread is not 5.5 inches, the Swash DS725 will not bolt on, whatever the listing says. If you cannot close your fingers on the fill valve nut, the T-adapter in the box has nowhere to go, and the LUXE Neo 120 is the wrong purchase until the maker names an alternate part for your toilet.
What should you do first?
- Measure the seat bolt spread centre to centre and note whether the bowl is round or elongated.
- Look under the tank: if the fill valve nut is exposed, a standard T-valve fits; if it is concealed, stop and read the maker’s compatibility page.
- Check the supply hose is flexible; if it is rigid pipe, budget a replacement hose with a 7/8 inch ballcock nut.
- For an electric seat, find a grounded GFCI outlet within 3.9 to 4 feet of the seat, or book an electrician.
- Pick the seat or attachment against those answers on the bidet attachment and bidet seat comparison.
Frequently asked questions
Does a bidet attachment fit a one-piece toilet?
Only if you can reach the fill valve nut under the tank. Brondell's Swash DS725 manual says many modern toilets have sleek designs that cover and camouflage the plumbing connections, which makes a standard install difficult or impossible, and it points to its alternate T-valve for those. LUXE and BioBidet manuals both install the T-adapter at the fill valve, not at the wall.
What thread size is the bidet T-valve?
The LUXE Neo 120 manual prints its T-adapter as 7/8 x 7/8 x 1/2 inch, and the BioBidet SlimGlow manual prints 7/8 x 7/8 x 3/8 inch: the two 7/8 inch ends go between the tank fill valve shank and the supply hose nut, and the smaller branch feeds the bidet. Both manuals say the T-valve installs at the tank, not at the wall shut-off.
Do I need an electrician for an electric bidet seat?
You need a grounded GFCI outlet the cord can reach. Brondell's DS725 manual says to use only a grounded GFCI outlet and a three-prong cord; BioBidet's Bliss BB-2000 manual requires a grounded 120 V GFCI outlet and prints a 4 foot cord. Adding or moving an outlet is electrical work for a licensed electrician, and all three makers say to consult one if grounding is unclear.
My toilet seat is round. Can I still get a bidet seat?
Yes, ordered in the round size. Brondell's DS725 manual lists the round seat at 19.5 inches long against 20.87 for elongated, and BioBidet's Bliss BB-2000 manual lists 18.9 inches round against 20.9 elongated. A non-electric attachment sits under your existing seat, so it does not come in bowl sizes, but the LUXE Neo 120 manual warns that a curved-lip seat can leave a gap.
Does a bidet attachment need hot water?
The two attachments whose manuals were read for this page do not. The LUXE Neo 120 manual describes a cold water, non-electric unit, and the BioBidet SlimGlow manual specifies a cold water source at 20 to 80 psi. Warm water on the seats named here comes from the electric seat's own heater, which is why those seats need the GFCI outlet.
Fact sheet and how to cite this page
- Answer
- A bidet fits when the seat bolt spread matches (Brondell’s Swash DS725 installs only on a 5.5 inch, 14 cm, spread), the bowl shape matches the seat ordered, the tank fill valve is reachable for the 7/8 inch T-valve, the supply hose is flexible, and an electric seat has a grounded GFCI outlet within its cord: 3.9 ft on TOTO’s SW3024, 4 ft on BioBidet’s Bliss BB-2000.
- Basis
- The makers’ own installation manuals: Brondell (Swash DS725), LUXE Bidet (Neo 120), BioBidet (SlimGlow and Bliss BB-2000) and TOTO (Washlet SW3024/SW3074). No code section is cited; the model codes are adopted locally and vary.
- Assumptions
- A gravity tank toilet with a seat bolted through two holes at the back of the bowl and a fill valve whose nut is visible under the tank. Wall-hung, tankless and pressure-assist toilets are outside this page.
- The bolt spread, seat length and cord figures are the ones each named manual prints for that model; other models from the same maker may differ, so read the manual for the seat you order.
- The skirted-toilet route (a T-valve at the wall shut-off instead of the fill valve) was found only on retailer pages, so this page describes the makers’ alternate parts and stops there.
- Method
- Five installation manuals read as PDFs on 30 September 2026: Brondell DS725 owner’s manual, LUXE Neo 120 owner’s manual, BioBidet SlimGlow and Bliss BB-2000 manuals, TOTO SW3024/SW3074 instruction manual. Each figure is attributed to the manual that prints it. Brondell’s help-center compatibility pages and two further TOTO manuals returned HTTP 403 and are not used.
- Primary source
- Brondell, Swash DS725 Owner's Manual (manufacturer or vendor document)
- Facts verified
- Last updated
- Cite as
- OwnerSpec, "Will a bidet fit my toilet? The five checks to run before buying an attachment or an electric seat", https://ownerspec.com/plumbing/guides/will-a-bidet-fit-my-toilet/, facts verified 30 September 2026.
Every figure above also appears, with its source, in the article. All sources ยท How OwnerSpec verifies numbers
Sources
- Brondell, Swash DS725 Owner's Manual (PDF) (manufacturer or vendor document)
- LUXE Bidet, NEO 120 Owner's Manual (PDF, Home Depot-hosted copy) (retailer listing or retailer-hosted document)
- BioBidet, SlimGlow User Manual (PDF, Home Depot-hosted copy) (retailer listing or retailer-hosted document)
- BioBidet, Bliss BB-2000 User Manual (PDF, Lowe's-hosted copy) (retailer listing or retailer-hosted document)
- TOTO, WASHLET SW3024/SW3074 Instruction Manual (PDF) (manufacturer or vendor document)