Toilet shutoff valve is leaking at the stem

A packing-nut adjustment might reduce a seep at the stem, but it won’t restore the valve’s ability to isolate the toilet. Since this valve is already stiff and won’t close fully, I wouldn’t rely on a temporary clamp or cap as a pressure-bearing repair, or assume the valve can safely be disassembled while the line is pressurized.

Plan to shut off the main supply before disconnecting the valve, and open a nearby faucet to relieve pressure. If the main shutoff doesn’t operate reliably, a plumber or the water utility may need to handle the isolation. A packing-nut adjustment is best treated as a limited attempt to slow the drip, not as a substitute for replacing the faulty shutoff.

A very small packing-nut adjustment may be reasonable to slow a stem drip temporarily, as long as the valve body and supply connection are not allowed to move. Stop if the stem binds more, the valve shifts, or the leak worsens. It will not restore reliable shutoff, so the main supply still needs to be isolated before replacing the valve.

Since the toilet valve won’t fully close, have you confirmed that the main shutoff actually stops the water before loosening any connection? If it doesn’t, I’d leave the toilet valve untouched and arrange proper upstream isolation rather than risk disconnecting it under pressure.

With the main shutoff closed, briefly open a faucet to relieve pressure. If water keeps flowing rather than tapering off, don’t disconnect the toilet line; arrange proper upstream isolation.

One caution worth adding: if that valve is old or corroded, be gentle with the packing nut. A slight snug can slow a stem drip, but forcing it on a stiff, aged valve risks cracking the stem or the valve body, which turns a slow drip into a real problem. Until the plumber arrives, simple containment (a towel and a small container, and a periodic check) is honestly fine for a slow drip. When it does get replaced, a quarter-turn ball valve makes the next shutoff far easier. And as others said, verify the main shutoff actually stops the water before anything gets disconnected.

A quarter-turn valve is convenient to operate, but that alone doesn’t guarantee it’ll be easier to shut off over time. The replacement’s compatibility and sound connections matter too.

When you say compatibility, is the existing connection threaded, compression, or soldered, and what size is it? That determines which shutoff can connect to the pipe without changing it or adding fittings. If you’re not sure, could the plumber confirm the connection before you buy a replacement?

A towel and container are reasonable only while the drip stays slow and is fully caught. If it becomes a stream or spray, escapes the container, or worsens after a gentle packing-nut adjustment, arrange faster service rather than keep waiting. Water reaching flooring, a wall, or nearby electrical equipment also makes waiting riskier. Is the drip still contained, or has it changed?

A compatible valve doesn’t necessarily mean the supply line also needs replacing. If the line is sound and the new shutoff connects properly, replacing just the failed valve avoids discarding usable material. Replace the line as well if it’s damaged or the replacement setup requires it.