Aplin was sent down to minor-league camp Sunday, Greg Johns of MLB.com reports.
Aplin was outrighted to Triple-A Tacoma on Monday.
Aplin was designated for assignment Friday.
Aplin was traded to the Mariners on Wednesday in exchange for a player to be named later or cash considerations, Ryan Divish of The Seattle Times reports.
The Astros designated Aplin for assignment Monday, Jake Kaplan of the Houston Chronicle reports.
Aplin was reassigned to minor league camp Wednesday, Julia Morales of ROOT Sports reports.
Aplin is a candidate to be removed from Houston's 40-man roster should the team need a spot during the offseason or spring training, Jake Kaplan of the Houston Chronicle reports.
Aplin has a .202/.313/.274 line after playing 39 games at Triple-A Fresno.
Aplin was assigned to Triple-A Fresno on Sunday, MLB.com's Brian McTaggart reports.
In 11 Grapefruit League appearances, Aplin is 4-for-22 (.182) with a double and an RBI for the Astros.