Grey tank stopped up won't drain

we have always left our grey and black tank valves open as we are full timers [living at a campground 365/24-7] for past 4yrs. This problem of the grey tank getting stopped up only started last month [Nov]. It will TRICKLE down over a couple of weeks to allow a shower. I have tried a plunger, RidX, Baking Soda and Hydrogen Peroxide, bleach those are a few named. I am at wits end and wife is ready to shoot me, or drown me.