The first step in answering a Sheila accurately, is understanding the question properly. Comprehensive knowledge of the Halacha alone is insufficient, as the Sheila as phrased will likely not fit neatly into the words of the Pri Megadim. Sometimes, a little creative thinking is required to get to the root of the situation and render an accurate Psak.
This Friday night during Kabbalas Shabbos, I was approached by a Yungerman with a Sheila. His wife had placed an onion in the Fleishig food-processor, and subsequently cooked it with the gefilte fish in a Milchig pot.
At first glance, it appeared obvious that the fish should be forbidden.
Though generally a clean knife would have no effect on an object cut with it, and a flavor absorbed for a full day is assumed to impart an exclusively negative taste; if that food has a sharp flavor, Halacha makes an exception to both of these principles.
With a food which has a strong flavor, such as an onion; we assume that not only can it draw out the primary taste absorbed in the knife, but it can even create issues when the flavor is not fresh. So, the Fleishig blade of the food-processor would render the onion Fleishig; even if the food-processor had not been used for meat for more than 24 hours prior to cutting the onion.
Furthermore, the same principle will cause the onion to draw out fresh Milchig flavor from the pot even if it was not used for dairy in more than a day. Since a raw onion at the beginning of the cooking process has a very sharp flavor, when it is cooked in an old pot it is capable of refreshing its absorbed flavors.
Consequently, the onion should be considered absolute Basar b’Chalav, and would forbid the gefilte fish as well.
However, after giving it a bit of thought, two practical considerations occurred to me.
First of all, how Fleishig really is the food-processor? Chances are it was used to chop liver and/or grate an onion cut with a Fleishig knife. If the liver was only chopped when cold, a thorough cleaning would be sufficient. Assuming the food-processor was clean when the onion was grated, there was no absorption of Fleishig taste in the blade for the onion to extract. Even if it was used for an onion cut with a Fleishig knife, there is a dispute among the Poskim whether an onion can extract flavor from one blade to impart it to a second. While the Magen Avraham is Machmir, the majority of Poskim are lenient.
Secondly, the onion was obviously not placed in the pot whole, as it had already passed through a food-processor. Presumably, it was grated in the food-processor and then mixed into the fish, eggs and ground carrots to create a fish loaf. Since the overall flavor of the fish mixture is probably not spicy, we would judge it as a single unit of non-spicy food which only becomes forbidden from a fresh taste.
Consequently, even though cooking will certainly extract flavor from the pot and impart it into the fish; if the pot was not used for Milchigs within the previous 24 hours, this stale flavor will not make the fish forbidden.
In conclusion, I informed the questioner that assuming his food-processor had never been used with meat that was Yad Soledes Bo, his gefilte fish was permitted even if the Milchig pot had been used with dairy within the 24 hours prior to cooking the fish in it. Even if it had once been utilized with hot meat (and even then it would only be a Davar Gush in a Kli Sheini, and probably only questionably Yad Soledes Bo), it would only be an issue if the pot was Ben Yomo.