Fining & Secondary

I'm looking at using a secondary fermentation and adding gelatin as a fining.

First, any thoughts on using gelatin.

Second, I currently have a 6gal primary and a 6gal priming.
Can I siphon the brew into the priming bucket, clean the primary, siphon back and add the fining? Or do I need a smaller (5 gal) fermenter for the secondary?
If I can reuse the primary, do I just need to rinse it out, or should I fully sanitize it before reusing?

TIA

If you don't have a second "primary", yes, do as you stated. It sounds like you don't have a carboy - is either of your containers clear? Clear will help a lot if you're using fining agents, so you can see when it truly has fallen clear.
Remember, too, that cold temp will help drop the yeast out so you can rack the beer off the yeast and start out with less yeast for the finings to work on. (hope you understood that last part).

Thanks LouT.

I don't have a carboy...yet. But will buy one if it really makes a difference. Wanted to try the fining first.

I have white buckets with spigots.

I guess I have/had a concern about the head space of normal air that will be in the fermenter when I turn it into the "secondary".
Will that create a problem?

Don't leave it in there too long, should be fine. I never used to even bother with a secondary, just racked it from primary to a bottling bucket right before bottling. You might consider doing such, too - just use the finings in your primary and when it settles out you can rack to bottling bucket and maybe cool that to settle out anything you accidentally transfered, and bottle it about an hour or 2 later...