I have not had to clean it yet and it's been about 2 or 3 months now. I usually empty it every 2 weeks or so and I check it for slime by rubbing the inside with my hand. I have had no issues at all, mostly because it's Maine and it's still cold here. I am sure that as it warms up I will have to use soap probably every week. The good thing about the bucket is that the water stays clean and between the water and the food my chickens can go a whole week without me doing anything but collecting eggs. Normally they are not left alone that long but we have taken a couple 4-6 day trips to Florida this winter and my pet sitter is not really a "bird" person so all she has to do is lift the top to the nesting boxes to get the eggs and not deal with the chickens. I have a camera in the coop that I can see over the internet and my phone so I can see if they have any food or water issues while I'm away and if they did than I can let my pet sitter know and only then will she have to deal with them. The IP camera is a great tool to have IMHO, I can see if there is a hen in a nesting box so I can wait until she is done to go collect rather than make multiple trips out there. My backyard is very muddy and wet so the less I walk on it the better until mud season is over.
One thing, you said you have the nipples for a line attachment, the nipples for the bucket are push in nipples and have a rubber gromit that goes in the hole first, this prevents the nipple from leaking.
You mentioned freezing, I don't know if you have electricity in your coop or not but if you do, just go buy a 25 or 50 watt submersible fish tank heater. It works great.