Obvious? Trust me, there is no "obvious" that you're missing here.
Far from being "obvious", working on/with tractors is more about being "innovative".
Maybe one of the answers from other members will already meet your needs. Great!
If not, maybe this will help:
I have just enough room under my tractor for a 5 gallon bucket. I have multiple buckets, so COULD, in theory, slide one out of the way as I slide another in. But sliding buckets on gravel is hard enough, and trying to slide a full bucket on gravel is...problematic (and messy).
I innovated a solution this way:
I took a length of metal flashing I had lying around, about 6 inches wide, cupped it so that it made a "trough". I line up 3 five gallon plastic buckets just outside the tractor body. I then hang (with some wire "ears") one end of my flashing "trough" just under the oil drain plug. The other end I position so that it is resting on the top of one of the buckets, so that anything that flows down will empty into the bucket. Before actually starting to drain things, I just make sure the bucket end is a bit lower than the drain-plug end, so things will flow the right direction. I then undo the drain plug, and let the oil drain. It flows down the "trough" and into the bucket. As the bucket fills, I just slide the bucket end of the "trough" (quickly) over to the next bucket, and the next. No mess. No moving buckets until the draining is complete. This has worked great for me.
If you don't have a straight path from the drain plug to where you can place your buckets, then you might want to invest ($) in a "Form-a-Funnel" (
Form a Funnel – No More Messy Oil Changes). They come in various lengths and sizes, and are flexible and bendable, so they let you create a channel over and around anything that may be between your drain and your bucket.
Good luck!
Edit: Oh yeah. Forgot to add this...
The flashing trough I use (or a Form-a-Funnel if you have one) also makes it so easy and CLEAN to change my oil filter. No more dripping over the frame, cables, or hoses, or leaking all over the place as I un-spin and remove the filter.