The Brazilian was pictured with his head down as he strolled into the Pall Mall Medical facility in Liverpool city centre.
It's understood the total deal being brokered could reach €56m, provided several add-on clauses are met on top of an initial down payment of around €39m.
The Brazilian only joined the Hornets past year, coming in for just £11.5m from Fluminense.
If Richarlison comes through his medical he is set to become the club's first signing of preseason.
The two Premier League clubs have a somewhat testing relationship, with Everton seeing an initial approach for Silva rebuffed after Ronald Koeman was sacked October 2017, and Watford eventually deciding to dispense with the Portuguese coach's services in January.
Richarlison, who attracted interest from Chelsea and Tottenham earlier last season, was left out of Watford's friendly with Fortuna Dusseldorf on Saturday as he finalised terms with Everton.
However, if he can rekindle and then sustain that sparkling form, he'll be a real asset at Everton, who are determined to break back into the top-6 under new boss Silva following a four-year absence.
Everton also hope to finalise the £18m signing of Lucas Digne from Barcelona after Brands travelled to Spain on Friday to finalise negotiations.
Everton are also looking to sign Barcelona central defender Yerry Mina, who impressed for Colombia at the World Cup in Russian Federation, although Wolves have now joined the race.