Power Soak 33638 SILVERWARE WASHER OWNER'S MANUAL - Manual (Page 24)

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If you have a stationary unit, permanent drain plumbing will have already
been installed.
Open the drain valve to release the spent water and detergent.
When all the dirty water has drained out, flush the tank with clean water to
remove any debris that remains.
Remove the drain screen by lifting it straight up and clean it in a scrap sink.
Close the drain valve, replace the drain screen, store the drain hose if
using a mobile unit, and replace the silverware basket. The pre-washer is
now ready to refill.