when doing an oil change on a driveway unless one has a suitable container that will hold more than 5ltrs then oil spillage is a norm. I thought will but a 8ltr container from ECP but those too are no good as the well fills up faster than the drain hole will cope. I now have a pump from lidl & have used it on a few motors. ( do it when oil is hot to speed process up ) I suck out approx. 2ltrs then let the rest out through the sump. Lidl have them on sale again very shortly .
I have one similar(bought from Machine Mart I think), and there are three bungs in it: the drain hole in the well, a large one on the neck to empty the contents, and a small one near the well. If I don't remove the small one, the well overflows as air inside the container has nowhere to go. I like this style of drain pan because I can just replace the bungs, and empty the pan at the local transfer station when it is convenient, without having to pour the oil into another container first.
Sucking
some of the oil is just another way of complicating a simple job.