k-meta and k-sorbate in the primary? in the keg?

i did several searches and found lots of helpful information, but not specifically the answer to my question so here goes.

let's say i want to backsweeten but i'd prefer to transfer from my primary straight to my serving keg (to avoid the ~15 minutes needed to clean and sanitize an extra carboy every batch). does anyone add potassium sorbate and potassium metabisulfite to the primary directly in order to kill off fermentation? i can see why this might not be so effective as there's a large amount of living yeast sitting at the bottom, but i 'm not too knowlegeable about these chemicals so i thought it was worth asking.

failing that, does anyone add those two directly to the keg? or does the cider need to be racked out of the container to which they were added?

these questions are motivated entirely by laziness so i'm not really hooked on the idea of either. but if either one is common practice and i just don't know it then it'll save me a little time and hassle.

sorry to bump a thread with no replies, but if i'm gonna do either of these it'll have to be in the next day or so.

i guess my real question is: do these two chemicals dissolve completely into the cider or do they do their work and precipitate out?

yeah man i did this very recently. i added the potassium sorbate and the campden right to the keg and racked onto the chemicals. i think the only difference from if you did it in a secondary is you will have to vent the keg a few times.

after everything is in the keg, i just let it sit as is for 24 hours. then i hit it with co2, shook the keg, vented, and repeated a bunch of times over the next day or so to let the gasses from the chemicals escape. i also added a can of concentrate (the whole of point of me using the campden and sorbate.) it worked for me- within a few weeks after carbing it, the cider was drinkable. and the concentrate improved the taste a lot.

its probably not the textbook way to do it, but it seems to work fine.