Regal 53 SC Owner's Manual page 147

Macerator (Overboard Discharge Pump)
To Use Macerator (If Installed):
Make sure it is legal to pump waste overboard
before starting the operation.
Open the seacock handle. It should be positioned
in line with the seacock as shown in the photo.
Activate the macerator breaker at the 12 volt salon
main DC control panel.
At the level monitor panel shown above turn the
key to the "on" position. With the key switch being held
in the "on" position push in on the macerator button to
start the opening cycle of the macerator interlock valve.
Once the interlock valve opens the overboard discharge
pump will begin to cycle. Continue to discharge the waste
until the monitor panel shows empty for the waste tank.
At this point, deactivate the macerator button
and key switch and turn macerator breaker to the "off "
position.
The interlock valve handle should now be at a 90
degree angle to the valve.
At this point you may desire to add an approved
holding tank deodorant by fl ushing the correct amount
down the toilet.
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Systems