Hmm, maybe I'm silly and blind. I didn't notice that there might be access panels behind the steps. I sort of crawled though the foot end of the port side bunk and tried to peek into the bilge, but found that I just can't get down there.
I didn't consider that the Commander didn't have a pump originally, but of course you guys are right. The idea of the plastic board sounds great. The PO simply recommended to replace the pump, but didn't say it was actually broken. So maybe I'll leave the old one in until it fails and get a new one ready in the meantime...
The diaphragm pump idea sounds good too, Ebb