I gotta get my two cents in on this one! I had the same problem untill I learned to take care of my "Cast-Iron". Learning the hard-way, I have found this:
Pre-heat the oven to 450-475 deg F.
When it is hot you may proceed:
A brand new cast-iron needs a good cleaning with hot, soapy water. Rinse, dry thouroughly and immediatly set onto a Med-Hi burner to heat up. As the moisture evaporates, begin to wipe the cast-iron with Crisco. Allow the Crisco to melt into the "pores". Work from the inside center outward. Include all surfaces, even the handle. When you think it is well coated, place in the oven for one hour, if you can stand it. Thirty min otherwise. Then turn the oven off. BUT..leave the cast-iron in the oven for all to cool.
WA-LA ! You have "seasoned" your cast-iron for the first time!
After my cast-iron has been "seasoned", it never again touches water.
I use it for "grease" stuff only.
It stays clean always, because, when done, I empty/scrape the cast-iron. And then follow with a good scrubbing My "scrubbing" is the pouring in of table salt, (is real cheap), and scrubbing with paper towels. I repeat as necessary.
Besides the cast-iron being real clean, it also has just been "germ-proofed" ! The salt does it.
On those occasions where my cast-iron gets, "violated", with water. I simply start all over.
Please note: The above process is a "hand" method, which must be performed from Start-to-Finish at one time. Any delay between the water and the greasing will allow rust to form. And that will be a taste you will not like.
Also, No Dishwashers for Cast-Iron. Period.