Jake
Ospho is good stuff. I usually apply it with as squirt/spray bottle like you buy in lawn and garden places. Don't set it to a fine spray and you don't have to yank on the trigger so hard as to create a mist. Just spritz it on.
I cannot find ospho anymore so I was able to get the same stuff at home depot in a gallon. it is usually called bare metal prep. All that metal prep stuff is basically phosphoric acid. it converts iron oxide to iron phosphate.
Anyhow you have to get yourself protected also.
Don't use it over a concrete floor, since any drips will immediately start eating the concrete.