You have scrubbed that line where the tub meets the wall. Toothbrush, paste of something, twenty minutes on your knees, and it goes pale for a day before the black comes back in exactly the same places. That is the tell. Dirt leaves when you scrub it. This does not, because it is not sitting on the caulk. It is growing in it.

So the effort was never the variable. A brush takes off the top layer of something with roots below the bristles, and the room hands it back everything it needs to regrow: warm, wet, and shut for most of the day. You are not losing because you are lazy. You are losing because the method is wrong.

This goes the other way. You spray it along the black seal and you leave the room. Nothing touches the surface. The colour goes while you are doing something else, and the line reads clean when you come back. The point is not the saved scrubbing. Pressure was never what reached into the caulk, so a method that does not need it gets further than your arm ever did.

One habit worth keeping. Bathrooms are small and you are shutting the door on this, so open the window while it sits and read the label before the first spray rather than after.

Here is the limit, and it is the one people buy this without hearing. It takes the stain out. It does not take out the reason the stain was there. If the fan does not work and the towels never dry, the black returns to the same seal on the same schedule, and a second bottle will not change that. The cause is air. Spray is not air.

Two more things it will not do. If the caulk is split, some of what you are looking at sits under the surface you can reach, so the face comes clean and a dark line stays in the crack. That is a re-caulk, not a clean. And this is a stain remover, not a shower cleaner. Soap film and water marks are still waiting for you.