PTFE that leaks is usually the wrong way round
I wrapped a tap tail in May and still had a weep at the thread. I added more tape. The weep moved. I undid the fitting and the tape was a wet rope, bunched at the first turn, bare thread after that. I had wound it against the way I tightened. Every turn of the spanner had unrolled it. I cleaned the thread, wrapped it the other way, four or five turns, tight in the grooves, and the joint went dry.
PTFE tape fills the gaps in a thread so the male and female can seal. It only stays there if you wind it in the direction you will tighten. Looking at the end of the male thread, that is usually clockwise, the same way the fitting will go on. The tape then beds in. Wound the other way, the fitting shoves it off. People add layers. Layers on a backwards wrap are a bigger rope that still comes off.
I start a couple of threads down so the first turn of the fitting can start clean. I keep the tape taut. Loose loops are lumps. I tear it and press the end down. I do not tape over old, wet tape. I take the old stuff off. A dirty thread with a new wrap is a leak you left in.
A tap that drips is usually the washer in the head is the spout, not the tail. If the drip is from the mouth of the tap, stay with the washer. If it is from a threaded join, stay with the tape and the direction. A bottle trap that weeps is usually the washer is a seat, not a thread. I do not PTFE a trap washer. An isolation valve that will not close is usually the slot is how I shut the water before I undo a tail. If I cannot isolate, I stop. I do not start on a live thread.
I do not tape a compression olive. The olive is the seal. Tape on an olive or on the pipe under a compression nut stops the olive biting and then you have a leak you cannot pull up. If a compression joint weeps, I stop and I do not hide it in tape. That is a different joint.
Skip wrapping until the thread looks like a bandage. A few tight turns in the grooves beat a fat white sausage. Skip tape on plastic bottle-trap threads. Skip tape on a washer face. Skip leaving a shred hanging that will wad in the first turn. Skip PTFE on a scored tap seat. The seat needs facing or the job is bigger than tape.
I use enough to fill, not enough to make the fitting hard to start. If I have to force the first turn, I have too much, or I am cross-threading. I back off and look. A crossed thread with tape on it weeps and then strips.
This shows the first time you use the tap after a Saturday job, or as a slow stain in the cupboard. I now wrap, assemble, isolate open, and watch before I put the basin contents back. A bead at the thread is still the wrap or the thread. I undo it once. I do not add a second colour of tape on top.
I do not need a new tap because the tail wept. I need the tape with the thread, clean metal, and an olive I have left alone.
If I later add a buy link here, it will be a paid promo.