Need a temporary greywater tank to get tags from DMV

[Wezeralus]

So my partner and I just finished getting our inspection and enhanced inspection work completed for our skoolie. We were just now informed that in order to get tags from the DMV (Pennsylvania), we still need to have a shower with greywater tank. We have a trip coming up in a few weeks and we need to drive our bus.
Does anyone have information on how to quickly set up a passable-looking, temporary greywater tank? We don’t even need it to be functional at the moment, we just need it to be passable to the DMV for our trip. We will worry about doing it properly after we’ve returned home. We will not be using the shower at all on our trip.

PS-we do have a few rain-collection barrels at home. Let me know if any of them (pictured) could be usable for this purpose.

[IWC Bus]

I have used a 55 gallon plastic barrel for my Black and gray tank with no problems.

[Wezeralus]

Where did you attach yours?