My furnace has burned 1,670 gals so far this season, i have cleaned the nozzle and replaced o-rings 3 times.
fly ash is all i have blown out a time er two, i'm yet to filter a drop. just let the totes settle for 3 or 4 months and pump them out leaving about 20gals in the bottom. my unit burns a wide variety of differnt oil as 80% of it comes from local recycling centers. WVO, drian oil, hydraulic, synthetic and i've even seen some oil based stain get dumped into there tanks.
It took some tweaking to get it dailed in as far as nozzle size, air pressure etc but now its a set it and forget deal. in the cold months it does not shut down for days at a time.
I use a thermostat for a jet heater to control the temp once the shop and stored oil is warm.