What do you guys do to make sure there is no crap gathering inside a set of used callipers?

Just whack 'em on and hope the bleeding process flushes out any contaminants?

Mainly done this on bikes, but I pull them apart, give them a good clean and paint, often a sand blast & paint, put a new seal kit in and rebuild with a smeer of rubber lube on the seals.

Because the. piston in calliper dosn't move much debris in callipers isn't much of a problem, it is more of problem with master cylinders.
The thing that would concern me with a second hand calliper would be if some idiot in the past had used WD40 and contaminated the seals.

Depends if they've been left "open" or not. I sold a set of calipers that I bought (recon) and then took off the vehicle - I'd left some fluid in them and put the red plug in the pipe attachment to stop crap getting in.

If they've been left exposed, then it can't do any harm to pop the moving parts out, clean and re-assemble with the correct red grease on the seals. You can determine if it needs new seals or not when it's apart....

[Edited on 5/2/14 by Charlie_Zetec]

Electrolysis brings them up like brand new..

I bought a set of reconned Sierra calipers and they were in worse condition than my 'cooked' ones.

Swapped the seals over and hey ho there you go!

Cheers guys