The meeting with the dead was considered risky. When one approached the dead, he'd rather remain silent, lest he could lose his voice. Moreover, the contact was deeply moving. That's why pilgrims underwent initiatory practices directed to prepare them to the event, both spiritually and physically.
People observed special diets, said their prayers and offered sacrifices as those described in the tenth canto of Odyssey.
In order to avoid death miasmas, people purified themselves with ablutions. So Ulysses, after the suitors' slaughter, burnt sulphur to purify the rooms smeared by his enemies' blood.
After the visit to the Nekromanteion, pilgrims purified themself again with water, like Alcestis who, returning from Hades, washed herself for three days to get free of the contagion danger. Still today in Thesprotia people coming back from a funeral, wash their hands with water and shake them thrice, letting water drop down and whisper "God forgive him".