To remove silicone caulk, use a Dap product called "Silicone-Be-Gone" which you should find in the paint and caulking aisle of your local home center. This product is really nothing more than gelled mineral spirits, and mineral spirits will SOFTEN cured silicone caulk. Mineral spirits will not dissolve cured silicone caulk, only soften it so that it can be removed by mechanical means, such as scrubbing with a Scotchbrite pad.

Often, people have trouble getting silicone caulk to stick to tub and tile after supposedly removing the old silicone caulk. The reason they're having a problem is that they haven't removed the old silicone caulk COMPLETELY. The way to tell if you've removed all of the old silicone is to wipe off the Silicone-Be-Gone with a damp sponge. Then sprinkle a fine powder like portland cement onto the area where the silicone caulk was and rub with your finger. The powder will become embedded in the soft silicone caulk, revealing the location of the remaining silicone caulk. Now, use the Silicone-Be-Gone on only the areas where there's remaining silicone caulk. Repeat this procedure until all of the portland cement powder wipes cleanly off tub and tile indicating there is no remaining silicone caulk. NOW, the new silicone caulk will stick well.

If you're having trouble removing mildew from old grout, the usual cause is that the bleach you're applying is not being drawn by capillary pressure INTO the grout, and the usual reason for this is that the porous surface of the grout is all clogged up with soap scum. Use a phosphoric acid based toilet bowl cleaner to dissolve that soap scum. Phosphoric acid toilet bowl cleaners will be gelled so that they're thicker. After applying the phosphoric acid, use a rubber squeegee to remove the toilet bowl cleaner to the grout lines and let it sit for a minute and then scrub the grout lines with an old denture brush or any stiff nylon bristle brush. That will remove the soap scum from the surface of the grout so that when the wet surface of the grout dries, it will wick bleach in by capillary pressure, and that's the key to cleaning grout with bleach.

If you're going to be cleaning mildew off silicone, it's important to have a STRONG and large spoon both for mixing the bleach and borax slurry and for scooping it out for spreading on the silicone with a teaspoon. Go to any place listed under "Restaurant Equipment & Supplies" in your yellow pages and buy a DESSERT SPOON for $2 or $3. The strongest spoon in any place setting will be the dessert spoon because it's meant for digging into hard ice cream and fudge. The tea spoon and soup spoon are weaker because they're meant for use with liquids; not for eating hard ice cream or fudge. You need a strong spoon like a dessert spoon to mash the borax against the side of the mixing container to make for a smooth and spreadable slurry.