For winterizing - open the sea-cok to drain any water, and leave it open. Disconnect the intake hose from the sea-cok and place a funnel in the hose. While running the pump, (spray nozzle open on coiled hose) pour in ant-freeze until it exits the nozzle.
If you want, you can add a permenant "t" fitting, (along with a plug or threaded cap) to the same hose between your sea-cok and pump intake. That way, any time you want to flush or winterize it, you just open up the "t" , attach a funnel and flush, but you keep the sea-cok closed. When your all done, open the sea-cok to drain.
As far as using it in freezing weather - I wouldn't risk it, especially in freash water, unless your prepared to do the above immediately afterwards. Opening the sea-cok, and draining the coiled hose is not enough because there's still water trapped in the pump, strainer and possibly other under deck hoses. Us salt water guys can get away with it a little longer, but only by a few degree's. Again, imo, it's not worth the risk.
Also, if you have a livewell, (with a 3 way valve) you want to flush that as well. Just work the valve back and forth a few times while pumping the anti-freeze. If you have a seperate pump and sea-cok set up for a livewell, do it the same way as the washdown method.
