I've been doing some lager fermentaions in 5 gallon Corny kegs. Less kausen forms with a lager than an ale that is really rocking the fermentation.
I do 10 gallon batches and split between 3 kegs, as i have enough kegs to do this. I fill by weight, adding about 27 to 28 lbs wort per keg. I use the gas in as my CO2 out. In my room in the basement that gets down to 50F in the winter i have a gas disconnects with tubing going to a bucket of sanitizer. In my temp controlled keezer i use spunding valves set to a low pressure.
One trick is to cut about 3/4 inch off of the beer dip tube. That way it is less likely yo clog, and you leave yeast behind when to transfer the beer off for lagering.
Transferring procedure is to have 2 clean, sanitized, and purged kegs ready. Make a black disconnect to black disconnect jumper. Do a closed transfer from the fermentation keg to the vented purged empty keg. I put a gas disconnect to bucket of sanizer on first to vent the pressure and act as an airlock. I transfer by weight on a scale, a full keg weighs 50 lbs. Pressurize when done. Put the 2 full kegs into the lagering chamber.
Hope this helps.