We were steaming at Steve's yesterday when he pulled out his Aster Berkshire which he had not run in a couple of months. It ran fine, but when he went to suck the water out of the oil tank it came out GREEN. UGH.Steve was appalled and we were ready to throw up. It seems that Steve was in the habit of not draining his oiler after each run, waiting instead to do that next time he ran the engine. As a result he was able to grow a nice crop of algae in the tank. He is now trying to clean the thing out and blow out the lines. Steam oil as I understand it contains lard so it was the perfect culture for growing a nice crop. Just posting this in case you are one of those that doesn't blow out your oil tank on a regular basis. Needless to say, we all went home and started to check out all our engines too even though the rest of us always cleaned out the tank after each run. I would think boilers are safe from this because they are filled with distilled water which is sterile, but if you aren't going to be running again for a long time perhaps you should drain it also. Happy Steaming.