I had the same problem in #45 when I got her , plus there was 6" of sludge at the bottom of the sump.Smelled like a skunk had died in there .
1st , get a wet/dry shopvac and suck all the water and crap out ( it will just clog a bilge pump).
2nd , pour in a gal of clean water and some pinesol or Simple Green or whatever and scrub with a toilet brush (long handled).
3rd , vacumn and rinse & repeat 'till she is sweet smelling .

With the vac you can get it completely dry , bilge pump will always leave a quart or 2 down there .