The pipes backed up on the lower levels of the stadium during Oakland's 10-2 victory, creating a stink and pools of water in the clubhouses used by both teams and the umpires.
The A's and Mariners moved to a higher floor and cleaned up postgame in the locker room occupied by the Oakland Raiders during NFL games.
Coliseum officials said the six-day homestand, which drew 171,756 fans, overtaxed the plumbing system at the 47-year-old stadium.
"Make sure everybody finds out about this sewage thing," Oakland starter A.J. Griffin said. "We need to get a new stadium."
The San Francisco Chronicle reported that leaking pipes and backed up drains occur often, even on days when the Coliseum is empty. The field is 22 feet below sea level, and the clubhouse level is 3 feet below sea level.
A's team president Michael Crowley told the Chronicle, "It's clear, right? This isn't the first time this has happened."
Several Mariners left without showering. Towels were used to block sewage from running into the players' general dressing area.
Seattle manager Eric Wedge's office had about a foot of liquid, forcing him to hold his postgame news conference in the hallway.
The A's, who start a road trip in Texas on Monday night, likely will have new carpeting when they return. The extent of the damage isn't known yet.
There were visible wet spots around every drain on the ground floor, though the main damage was to the locker rooms and storage areas.