I use clay pots and it seems ok. Pots are clay that had been fired to 'fuse' the particles. There are still salts, but washing and soaking should do it. They can behave like ion exchangers, so my bet would be a few rounds of washing. Small quantities of salt can slowly exchange with the soil but that might be useful to the plant. Acetic acid is a weaker acid than the acid that formed the conjugate base phosphate and sulphate salt. So it might be difficult to displace say MgSO4 to Mg(CH3COO)2, though I have never tried it. I just wash and soak and wash and soak until i feel that the pot is ok. Not very scientific
