Do I need to cut into the wall or add a drain?

No, and this is where the guides you will find go wrong. They are describing a standalone porcelain bidet, a second fixture that sits beside the toilet with its own waste pipe and floor bolts. That is a European bathroom. What almost everyone here means by a bidet is the handheld spray on a hose, which takes its water from the toilet supply through a T-valve and drains into the toilet you are already sitting on. Nothing is cut and nothing is added.

What if my toilet has no tank?

Then the T-valve goes on whatever supply line you do have, usually the one feeding the pail tap. The principle does not change: you are teeing off an existing cold supply and putting a valve in the branch. If there is no accessible supply line at all, which happens with some older pail-flush setups, a spray means running a new line and that is a job rather than an afternoon.

It leaks at the T-valve. What did I do wrong?

Almost always one of two things. Either the rubber washer that came with the fitting is missing or sitting crooked, or the plastic thread has been overtightened and cracked. These fittings want hand tight and then a short nudge with a spanner, no more. Thread tape belongs on tapered metal threads, not on a joint that seals with a washer, and wrapping tape around a washer joint is a common way to make it worse.

The spray dribbles instead of spraying.

That is pressure, not the spray. A bidet head needs a reasonable flow to work properly, and if your house runs on gravity from a low tank there may not be much to give it. Check whether your taps are also weak before replacing the head.

Fitting a bidet spray is a twenty-minute job

A T-valve, a hose and a head. Nothing is cut, nothing is drilled, and nothing new drains anywhere. Here is the whole of it.

Call 0920 960 0596 Faucet and shower work

The guides online are fitting a different thing entirely

Search this and you get Home Depot, Ferguson, Lowes and Victorian Plumbing, and every one of them is installing a bidet as a SEPARATE PORCELAIN FIXTURE. Home Depot tells you to align it over the drain and mark the hold-down bolts. Ferguson tells you to attach the drain fittings. Victorian Plumbing tells you to secure it to the floor brackets.

That is a European bathroom with a second basin beside the toilet. What everyone here means by a bidet is the handheld spray on a hose: no drain, no bolts, no waste pipe and no second fixture. It takes water from the toilet supply and drains into the toilet you are already sitting on.

What you need

A T-valve, also sold as a three-way adapter, sized to your supply
A braided bidet hose and the spray head, usually sold together
The rubber washers that come with them, all of them
An adjustable spanner, a pail and a cloth

The five steps

1. Close the supply and empty the line

Close the small valve on the pipe feeding the toilet if you have one, or the main if you do not. Flush to empty the tank, and keep a pail and a cloth under the joint you are about to open, because there is always more water left in there than you expect.

2. Take off the hose that feeds the tank

Undo the flexible hose where it meets the bottom of the tank. On a pail-flush setup, undo the connection at the tap instead. Look at the washer inside the nut before you put anything back: if it is flattened or split, replace it while you are there.

3. Fit the T-valve

The T-valve, sometimes sold as a three-way adapter, goes between the supply and the tank. Supply into the bottom, tank hose back onto the top, bidet hose onto the side outlet. Hand tight, then a short nudge. These are plastic threads sealing on rubber washers and they will crack if you treat them like steel.

4. Connect the hose and the head

Braided hose from the T-valve side outlet to the spray head, washers at both ends. Route it so it does not kink behind the bowl, which is the usual reason a new spray feels weak.

5. Open slowly and watch every joint

Open the valve a quarter turn and wait. Run a dry finger around each joint rather than looking, because a slow weep is easier to feel than to see. Then open fully, let the tank fill, and check again after a few minutes under full pressure.

If your toilet has no tank

Plenty here do not, and it changes very little. The T-valve goes on whatever cold supply you have, usually the line feeding the pail tap, and everything after that is the same. You are teeing off an existing supply and putting a valve in the branch.

The one case where it stops being simple is a bathroom with no accessible supply line at all, which happens with some older pail-flush setups. Then a spray means running a new line, and that is a job rather than an afternoon.

When it is worth ringing somebody

No accessible supply line, so a new one has to be run and probably chased into a wall.
A concealed cistern behind tiling, where getting to the connection is most of the work.
A joint that still weeps after the washer has been checked and the fitting is hand tight plus a nudge. Do not keep tightening it; that is how a plastic thread splits.
A spray that dribbles when the rest of the house is also weak, which is a pressure problem rather than a bidet problem.

Questions about fitting a bidet spray

Do I need to cut into the wall or add a drain?: No, and this is where the guides you will find go wrong. They are describing a standalone porcelain bidet, a second fixture that sits beside the toilet with its own waste pipe and floor bolts. That is a European bathroom. What almost everyone here means by a bidet is the handheld spray on a hose, which takes its water from the toilet supply through a T-valve and drains into the toilet you are already sitting on. Nothing is cut and nothing is added.
What if my toilet has no tank?: Then the T-valve goes on whatever supply line you do have, usually the one feeding the pail tap. The principle does not change: you are teeing off an existing cold supply and putting a valve in the branch. If there is no accessible supply line at all, which happens with some older pail-flush setups, a spray means running a new line and that is a job rather than an afternoon.
It leaks at the T-valve. What did I do wrong?: Almost always one of two things. Either the rubber washer that came with the fitting is missing or sitting crooked, or the plastic thread has been overtightened and cracked. These fittings want hand tight and then a short nudge with a spanner, no more. Thread tape belongs on tapered metal threads, not on a joint that seals with a washer, and wrapping tape around a washer joint is a common way to make it worse.
The spray dribbles instead of spraying.: That is pressure, not the spray. A bidet head needs a reasonable flow to work properly, and if your house runs on gravity from a low tank there may not be much to give it. Check whether your taps are also weak before replacing the head.

Most people will not need us for this

It is genuinely a twenty-minute job. Ring us if the supply line is not where it should be, or if a joint will not stop weeping.

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