Hello, I know some do not eat dairy and fish (I do mean dairy and fish not dairy and meat) together. If this is the case, what must be done in between? If one has fish for dinner, would it be sufficient to eat or drink something neutral before having milk the next day? And would one need separate toothbrushes?
The Ashkenazi custom (and I assume that you are of Ashkenazi decent) is not to be concerned about this. For the Ashkenazim, they can eat a tuna casserole with cheese inside it without a problem. Obviously there is no need to wait. For Sefardim who don’t eat the two together, they may eat one right after the other, however it is preferable that they wash and rinse their mouth out between the two.
Darcei Moshe Y:D 87-4, Taz Y:D 87-3, Shach 87-5, Magen Avrohom O:CH 173, Aruch Hashulchan Y:D 87-15Kaf Hachayim O:Ch 173-3.