I don't have Sebastopols, but I do have Embdens, Toulouse and Pekin ducks. With the weather we've been having lately, almost down to zero, then in the 40s, then snowing, then raining.... My ducks started to look like 'swamp' ducks and the Embdens were getting just a bit grubby around the edges.
Everyday it's above freezing, very important, I put warm water into a large trough for them. I run a hose out to them from my kitchen faucet so I can make sure it is warm enough for them to really want to get into it. Most of them will use it, but please if you try this, make sure it's above freezing. My Chinese decided to make use of the tub one day when the temp was only 8 degrees and had frozen feathers afterwards. Not cool, but put him under a heat lamp for a bit and he was just fine. Lesson learned.....no bathing unless the sun is out and temps are well above freezing! Good luck!