Something I`ve learned from lake diving is that if there is no freshwater rinse available at your entry/exit locale, supply your own post-dive rinse in a water bottle or 1 gallon jug.
A 1 gallon jug should provide you enough water to rinse most everything off prior to turning off the lines, purging, and tear down. Hopefully this will help clear up some of the issue.
Another idea is if you have a gear tub that you use for transporting your gear to/from the site, they can make great rinse tubs prior to tear down. But again, you may have to provide your own water.
I have 2 cheats at my disposal. I own a portable camp shower and have a dive box I can use to dunk/rinse if needed.