Replacing grout/caulking in bathtub?

Take it all out. A patch job is never worth it.

Once you have it all out, spray it with Tilex and rinse it out really well.

Use your blow dryer to dry it out really well and let it sit for at least a day.

In the meantime, use masking or painters tape to mask the tub and the tile 1/4" from the grout line.

This way you can get a really neat edge.

Buy silicone sealant for TUB AND TILE. It is specifically for this job. Don't use anything else. It stays rubbery and is mildew resistant.

Before starting, fill your tub with water to weigh it down, the tub does move a bit when it's full.

Run a bead of silicone in the crack, over filling it SLIGHTLY.

With a WET finger, smooth the bead so it is a concave shape. Don't worry about the extra stuff that collects on the tape.

When the whole bead is done and it's smooth to your liking. Take the tape off while the silicone is still soft. Do it in a one smooth motion and dispose of it immediately.

Let the silicone dry , with the tub still full of water, until it is hard. DO NOT stick your finger in it to test it. Put some silicone on a piece of scrap paper for a test piece. When that piece is fully cured, you can drain your tub and you're done.

it's called caulk, grout is what's between the tiles

take a utility blade with holder and remove caulk

wash down with varsol or some other cleaner

if you are not experienced tape with making tape

and caulk remove tape good as new

from a old timer