What is the law if one placed a hot cover of a cooking pot of fish on a cooking hot pot of meat or poultry?
 The reason: As the taste of fish absorbed in the cover does not prohibit the meat, as brought in Taz 116/2 regarding the allowance to cook fish/meat in a meat/fish pot that is Ben Yomo. Furthermore, even if there was fish gravy condensation on the cover, and this condensation then fell into the meat, one can surely assume that there is 60x against it and it is hence permitted.
 As the cover most likely contained fish condensation on its bottom and has now become forbidden due to the meat vapor that became mixed with it. Now, although when one has cooks meat with fish some Poskim rule the pot becomes forbidden and must be Kashered, nevertheless the final stance on this subject is that waiting 24 hours is suffice. [See Darkei Teshuvah 116/28; Kaf Hachaim 116/13]