fermentation bucket query

[hare1975]

Sorry to be stupid or ignorant, i have been brewing from kits for well over a year now, and still tend to do things strictly by the book. I have a couple of questions that i would like the answers to.
Firstly. If i am brewing consistantly do i have to sanitise the fermentation bucket if i do a brew straight after bottling. And if not. Can i leave the dregs at the bottom of bucket.
Secondly. I have 2 king kegs that i do not use, as tend to do the coopers lagers and struggle to get kegs chilled, i find bottling gives better fizz for lager. My question is, could i use a king keg for primary ferment, if my other bucket is in use, or should i get another bucket? If i can use a keg i assume it will release excess gas through the valve, or would i need to periodically loosen lid in place of an airlock. I know these are maybe silly questions but advise would help me no end.
Many thanks :

 

[Awolphotography]

I would always sterilise, and if using the yeast from a previous brew move some if ha into a lean bucket.
I wouldn't use a king keg for primary, pressure affects yeast and the pressure required to vent the keg will almost certainly have already had a negative affect on the yeast. If I were you I'd sell the king kegs and invest it in stuff you are going to use...