1. Turn off valve going to DWC for entire rack.
  2. With wet vac connected to floor drain (or sump pump), pump out the full volume of water in the tray.
  3. The purge pump still running, use hose connected to sink (or faucet on back wall near the computer) to fill in fresh water. Prop x3 corners of the tray so all the water flows to one lowest corner and is pumped out.
  4. Use a side towel with peroxide dilution (and rubber gloves) to wipe down the walls and sides of the tray where algae might grow. Remove any debris by hand paying close attention to the plumbing stand pipes.
  5. Remove tray props, return plumbing to original configuration, remove the purge pump, turn the ceiling valve back on and allow the tray to fill up from central feed.