No need to lubricate a joker valve.
Only MOVING parts require lubrication, to insulate them from wear due to friction...a joker valve isn't a moving part, it's just a rubber "cup" that has a slit in it. Because that slit stretches with use, joker valves should be replaced at least every two year...but don't expect a new joker valve to solve your backflow problem for very long...it's not designed to prevent slow seepage, only a flood. Once waste has gone through it a dozen times, the slit no longer closes tight (over a couple of years, it ceases to be a slit and becomes just a hole--which is why they need to be replaced every couple of years). If the head discharge hose is an uphill run out of the toilet, the best you can do is make sure to flush long enough (manual toilets, use the dry setting) to ensure that what's running back is only clean water.
