Sticky waste tank valves

On my RV. I have noticed the waste gate valves have become very sticky especially on the grey tank. I'm guessing the soap and cleaner build-up are causing the valves to gum-up and stick. I poured appox. 10 ozs. of baby oil down the sink drain into the into the grey tank after I emptied the tank. The valve now slides at the touch rather than pulling and trying to force the valve close. The black tank will get treated next when it's time to drain it.