If anyone's interested, the Mercy Relief sorting centre is in a former school. Get off at Kovan MRT station and walk down Lowland Road. Here's the tricky bit: the front gate is unmarked except for a crudely-stenciled "58" on it. There's also construction activity going on right outside, so don't let that fool you. Just remember that the school is at the bend in Lowland Road.
Don't bother asking the people who live around the area. They will all direct you to "Helping Hands" -- but they're also helping out with supplies for tsunami victims so it's all good. They stop work at 8.30pm though.