I've just the two, I can't seem to hold on to them for very long before horse food makes it into them and then they never make it back inside able to hold water again. My mare has a destruction fetish it seems.
^When you say salt mix buckets, do you mean you dose each bucket with salt?
You should try for a small tub or vat. It's much easier. You can find 55 gallon drums on CL, quite often for very cheap.