Easy and effective way to clean a very dirty plastic broom

Here's my 0.02:

For starters, check with the refrigerator manufacturer for official cleaning instructions. Some have explicit cleaning instructions/restrictions.

Try basic cleaning first (a good how-to is available here: http://www.ehow.com/how_92_clean-refrigerator.html).

Assuming that doesn't do the trick, you can try bleach but be careful. Another good how-to is available here: http://www.associatedcontent.com/article/2489239/how_to_clean_a_moldy_refrigerator.html

-M

Is this a finished concrete floor or raw slab? If slab, I'd suggest low-power pressure wash...maybe even start with just the garden-hose attachment. Add a bit of soap.

The real challenge, however, is that you have no drains. I can't think of an easy way to get around that short of power wash a bit, shop vac it up, and then constantly repeat until the shop vac is full, then empty that into a sink and repeat.