I have the 4" tube setup for doing legs. Started with a gallon of Evapo and have been topping it off with white Vinegar. Been using the same rig for two years now. Probably done 50 sets of legs and anything else I can put in it. Never dump out the mix. Once in a while I run it through a strainer to clean out the gook.
Probably more vinegar the evapo by now. Still works great. Usually leave legs in for a week. No rubbing needed to get any rust off.