These medications may also be used to treat thyroid cancer or other thyroid conditions. The long-term safety of levothyroxine is well established. Typically side effects only occur due to overdosage of the medication. For more specific information, consult with your doctor or pharmacist for guidance based on your specific condition and current medications.
My neighbor just puts 3-4 gal of bleach down the pipe, then waits 24 hrs. Then runs water through all the fixtures until the bleach smell is gone. He said it usually last for 1-1/2 years. Our water is relatively soft, but does have a bit of iron in it.
However, most people - and for good reason - don't want to wait that long. It's too easy for there to be something spilled on it. If you really want to do a bang-up job, do your first application of sealant after 48 hours. Then, 30 days later, clean the grout with a toothbrush, using a strong mix of bleach & water.