I have a bathtub with a tiny tiny crack near the drain. It looks like it used to be covered up with some sort of putty or caulk that surrounded the drain which has gradually worn away over time. What can I use to replace that seal around the drain? Is that the proper way to seal the crack?

The appropriate patch material depends in large part upon what material the tub is made of. Some tub materials cannot be patched reliably and are just ruined if they crack. Caulk or putty is only a temporary fix for a crack near the drain no matter what the material is.

You can perhaps use an epoxy resin on it or some sort of hardening crack sealer, especially if it is a fiberglass/composite tub material. However, the chances are unfortunately good that the crack will always be there and you just need to replace it or keep patching it every few years.

Look at your phonebook under Porcelain repair. This professional can repair any kind of cracks and match it with the same color. It can cost upto $100.

mcneilja............

I wonder if the crack you're refering to is around the drain itself...........The junction between tub and metal drain.........

OR....... do you have a crack in the tub like Lawrence and the SurfaceDr have guessed.......

If its fiberglass, you can have a fiberglass repairman come out and repair the area. Many tubs are damaged in shipping, the manufacturers use these repairmen to fix the problems. The repair is done so well you can't even tell it was done. Check with your local plumbing wholesaler for who they use. If its porceline, you can repair it, but it won't last.
Good Luck
Raymond