Shower sump drain pump

Apr 3, 2012
95
Catalina 309 Sydney
Happy new year...

Every time we try to drain the shower sump I have to prime the pump to get it going,
The pump is under the v berth so it's a real pain if the bed is made up. (every time ..!)

Is there a trick to get this pump working ?.

most of the time we use the transom shower but occasionally the one in the head.

Once I fluked it by flushing the head, but I can't remember the sequence that made that happen