For the Sprinter oil changes I use a Fumoto drain valve plug and a 2.5 gallon gas can to catch the oil. Initially I had a drain hose connected to the Fumoto valve and put that into the gas can to drain the oil, but as it turned out I can just stick the flexible spout hose from the can right into the Fumoto valve. Never spill a drop.
I got that idea from when we had an RV with an Onan RV QD 8000 diesel generator and used a Fumoto drain valve with a drain hose going to a 1-gallon gas can.
We used the same synthetic oil in the generator that we used in the RV. We used a Wix/NAPA oil filter most of the time. While truck, car and RV engines are designed for longer oil change intervals with synthetic oil, generator and other small engines generally are not. In that generator, 3 quarts of oil is simply not enough oil to provide both the lubrication necessary and have enough left over for for a "wash reservoir" to keep contaminants suspended for extended intervals. Change it at 150 hours (after the first 50 hour change, of course). In a pinch (raining, snowing, just an all-around nasty day) you can extended it to 175 hours, especially if you use a good synthetic oil and a good filter, but I wouldn't make it a habit.
You can use synthetic or dino oil, and many use dino oil rather than synthetic simply because you are going to change it every 150 hours regardless, and they don't see the benefits of the more expensive oil. But it's only 3 quarts, and using synthetic will not only let the generator run quieter, it will use less fuel. Most of those who stick with dino oil over synthetic are the casual RV crowd who camp one or two weekends a year and/or are mostly hooked up to shore power, and rarely even get 150 hours out of their generator in a year.
You would use synthetic oil to better preserve the engine, rather than to achieve the same engine wear via extended intervals. Frankly, repair expenses on a generator, especially on an Onan is just crazy (Onan sees you coming) and it's better to protect and preserve the motor with synthetic every 150 hours than it is to try and use synthetic to extend the interval.
Also keep in mind that when operating the generator in very hot (95° F or hotter) and in dusty conditions, the oil and filter should be changed more often than 150 hours, closer to 125 or fewer hours. In the summer, especially if you run the generator a lot while driving or a lot during the day, I'd go 125 hours, maybe even 100 hours. With a Fumoto drain valve and a drain hose it's like a 10 minute oil change, if that long. It's well worth the time to keep that engine protected and as preserved as possible.
Just some things to ponder.
