Watering the grass
Tee hee. Remember once I landed at a small airfield in France for just that purpose. Now usually on a Monday one doesn't even see the airfield cat, so I taxied clear of the runway, shut down and clambered out, was about to do the needful when I got a friendly greeting from the clean up crew who were tidying up after the previous day's air show. Took fully ten painful minutes chat before being escorted to the clubhouse to use the appropriate facilities, followed by coffee and cakes.
Don't think I would have the nerve to drop in on a private strip for anything so banal, though.