His mother Elaine, 53, and dad John, 52, led mourners who were paying their last respects at Michael's funeral service.
Police recovered the 23-year-old's body from the River Clyde almost a week after he went missing after a night out in Glasgow.
Since his body was found, almost £7000 has been raised for a memorial fund set up by the electrician's friends.
Mr Slaven said the money will be used to build a memorial to his son.
Mourners, including brother Shaun, 20, and sisters Paula, 25, and Monica, 21, attended yesterday's service.
Hundreds of family and friends also gathered at St Peter's Church, in Bellsmyre, Dumbarton.
Michael, from Dumbarton, left the Sugar Cube nightclub in Queen Street, Glasgow, shortly after 2am on Friday, August 30.
CCTV images showed him in a Subway sandwich shop, then acting erratically at about 2.30am in nearby St Enoch Square.
His dad John Slaven, said: "We are never going to know what really happened to Michael, and that makes everything even more difficult."
His father revealed toxicology tests have been carried out on Michael's body after the family raised fears that his drink may have been spiked.
However, the test results are not expected to be reported for between six and eight weeks.