I flushed (acid washed) the radiator on my Kubota last year. Here are some take-aways:
*) I used a commercially available flush from WallyMart and followed the instructions by using the machine for some time while the acid was in the system.
*) The first THREE 'rinses' were rusty-coulred
(A 'rinse' is: Fill with clean water, run for several minutes and drain)
*) My last several rinses were done using DISTILLED WATER so there was no chance of tap-water being in the system.
*) I kept up the rinse/drain cycles until they came out clear.
*) Each time I drained, I used leaf-blower into radiator-cap while the drains were removed. This extracted a SURPRISING amount of additional water.
REMINDER: If you do not use 'premixed' antifreeze.... ONLY mix with distilled water to achieve the 50/50 mix.
NOTE: If you have not opened the drains for several years, beware that they may be stuck or not even drain when opened. Be CAREFUL to not break off the drains while trying to get them open. If they do not drain, try spinning a drill-bit BY HAND into it to clear the clog.