Using a pot that has not been used for 30 days:[1]

One should not eat food that was cooked in a pot that had not been used for cooking for 30 days.[2] However, the world is not careful in this matter.[3] [Practically, the danger is only applicable if one did not wash the pot prior to use after 30 days, if however one washed the pot prior to using it then there is no danger involved in eating a food that was cooked in it even after 30 days of nonuse.[4] Likewise, the danger is only applicable if one eats the food directly from the pot. If, however, one first pours the content into a second vessel, such as a plate, and eats it from there, then there is no danger involved.[5]]

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[1] See Kaf Hachaim Y.D 116:143; Sefer Shemiras Haguf Vihanefesh [Lerner] 6:3

[2] Tzavas Rebbe Eliezer Hagadol-Orchos Chaim 64; Shemiras Hanefesh 32 [27]; Yifei Laleiv 3:11; Kaf Hachaim ibid; Darkei Teshuvah 116:69; Even Segula in Sefer Segulas Yisrael

[3] Shemira Meialya 32:13 [12] as can be seen from the fact that we have Pesach Keilim from year to year; Yifei Laleiv 3:11 in name of Or Chadash 8; Kaf Hachaim ibid; Darkei Teshuvah 116:69; See Shulchan Chaiy 15 that the above ruling is not literal and that one may rely on this

[4] Kaf Hachaim ibid; See Shulchan Chaiy 15 footnote 1 that one should first cook water in it, or clean it with hot water

[5] Mili Dechasidusa in name of his father in law; Darkei Teshuvah 116:69