What lube works best in TRS drive ? Also should or can it be filtered ? Whats the best way to flush out upper resivor ?

Take the hose off and flush it with WD 40 .
Drain it and take the cover off then clean it !!

I always use merc oil the green high prformance stuff ,never had any problem with it !!

Mercury High Performance Gear Lube.$16 X 4 !! I see why you would like to filter it. I don't know ,I guess you could as long as it looked pretty good to start with and wasn't really old.Them TRS's are getting to hard to find parts for to skimp on gear lube.You could maybe filter it through cheese cloth.It would take a really long time though.As far as flushing your reservoir you can remove the cover off it (the part the dipstick is connected to) and clean it out that way real well.I believe there are 8 screws holding it on which take a allen wrench.Try not to damage the gasket when removing it because they are no longer available.However you could make one yourself if you had to,their a pretty simple gasket.

I wasent lookin to filter old oil . Was thinkin that with all the trouble with gears that while running and the new gears and bearings would last longer if they didnt run over any more junk than they have too. The magnetic plugs seems kinda wimpy but maybe thats enough.

I have run Royal Purple 75-90 for the last 8 years in my TRS. only failure was I only put 1.5qts in instead of 3 in one drive. and only had an upper failure lower survived.