How often do I need to flush the sump pit with water? That is, pour water into it from a hose to change the water.
Also, can I do it in freezing temperatures? Inside the garage the temperature is about 10C but outside it's freezing.
The sump pump is not inside my garage but that of my neighbour.
If you notice things growing in there or bugs breeding, a bit of soap (liquid dish detergent would be my first choice) will usually do in the bugs by altering the surface tension, and chlorine bleach will kill off bacterial slimes if there's not too much water flow (so it stays put for a while.) If there is water flow it should never get too nasty.
If you are not experiencing problems/smells, leave it alone - or perhaps put a cover over it if it lacks one, which will keep things from going into it and causing problems (small animals drowning, for instance - or the bugs that might want to breed in there.) If it also serves as a floor drain, put a screened section in the cover to allow water to flow in.
Ecnerwal's right. You don't need to flush your sump pail as a matter of routine maintenance unless pests or odors are a problem. If that's the case, "as needed" is your answer.
That said, I empty my sump pail seasonally. My particular property doesn't produce groundwater at the foundation after mid-autumn. I use a wet-dry vacuum to remove the water that the sump pump doesn't, allowing the pail to dry and remain sanitary. Because the sump pump's float only engages at water depths of about 8 inches or more, some water would likely remain all winter, possibly growing mildew and sustaining insects.
