My way is.
Empty, completely the bildge ( manually )
Turn off the bilge pump switch
Then dilute the 2 dishwashing tablets inside the sink with hot water, plenty 20-25 literes
Open the sink
Put more 50 liters of hot water
Wait 1/2 hour
The turn on the bilge pump switch
15/15 days, Ok ?
By the way my second bilge pump is a
Johnson Viking Power 24 V pump