how far do you tear down a reel when going to put it in an ultrasonic cleaner?

Down to the frame. Remove as much grease and dirt as you can before putting the parts in to keep the solvent cleaner longer.

how far do you tear down a reel when going to put it in an ultrasonic cleaner?

You do a complete brake down.

You will have to hand scrub some of the parts no matter how or what kind of tank you use.

We started with a ultrasonic tank back in the 80's when we started out, we soon found we needed a filtered system.

The only way we didn't transfer dirt to other reels/parts.

Good Luck & Tight Lines!

Seems like I've read you can put spool bearings in a jar of cleaning solution then put jar and all in with the rest of the parts to be cleaned without the fear of cross contamination.  Is this even possible? 

Steve

I put all metal parts,including bearings (with non - metallic shields removed if needed) in a glass jar of acetone to soak. Non - metallic parts get washed with diluted Simple Green.

I use small glass jars that contacts come in. They work great for small bearings. I use a small baby food jar for bigger bearings. I use medicine dropper to suck up a small amount of acetone and squirt in the jar. I then set the jar in the sonic cleaner with the fluid level lower than the cap on the jar. It only takes a minute or two for the the acetone to get very dirty on the first pass. Dump the acetone and refill with fresh acetone. Repeat the process until the acetone stays clear. This usually takes 3 times for most bearings. The whole process takes less than 10 minutes to have completly clean bearings. As bilgerat said, make sure you don't have rubber or plastic seals or shields. Those bearings can be cleaned the same way with diluted simple green, but it takes longer.