Japanese bowl with nesting upper bowl with drain hole in bottom?

Just purchased at auction a Satsuma bowl. The bottom portion is beautifully painted. There in a nesting upper bowl which is less ornate and has a hole in the bottom about 1″ diameter.

Anyone know the use of such a bowl?

Rare Roto Grip SD 73 Classic
$245.00 (0 Bids)
End Date: Friday Apr-18-2014 14:23:17 PDT
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