Will this work on cedar siding on my house to remove paint? Also will it work on my 500 gallon oil drum?

I used mine on both horizontal and vertical surfaces. It's a bit more work on a vertical surface, but not anything worse than using a regular tip. As far as paint removal goes, you'd need to test that for yourself. That would depend on the paint adhesion. What this WILL do for you however, is reduce the chances of damage to your wood from excessive pressure. So it's a blessing and a curse in that respect, I suppose.

It would be very hard to hold this against siding or an oil drum. If it's not flush to a surface, it tends to "buck" up on edge because of the strong water pressure. It needs the flush service so it can "float" on a cushion of water. The nozzle/wand of a pressure washer would work better by themselves I would think.

I would not use it on the ceder siding, ceder siding is soft wood, may cut it to it.

Oh it'll remove the paint from the siding and half the siding also. Cedar, when rough sawn is not burnished so the fibers will get eaten away. Did that once years ago and paid the price to replace half a house worth of siding. You can, however, use a light spray to get off the flaking paint but not down to bare cedar. As for the use on the oil storage tank, I wouldn't recommend it. The unit was designed for horizontal surfaces, patios, pavers, drives and sidewalks. Once it goes vertical it is difficult to handle . Use the spray nozzles.