I don't know why I didn't think of this earlier.

I am a private pilot. I fly alone most of the time. I'm the only pilot aboard all of the time. When I have to pee, I cannot just get up and go to a restroom - there's none in a small plane. It's impractical to land to use a restroom which might be far away or in a big crowded airport. I can't just pull over into a rest area.

When I first asked about the issue, I was introduced to a "Pilot's Comfort Station" which comes packaged for the great relief of either male or female pilots.

These are for big boys and girls. They are not expensive. They can be cleaned easily. They can be re-used before emptying. They can be sealed against spills due to tipping. They don't take up much space. They can be carried into a bedroom. They are odour free when used according to instructions. There are no consumable expenses. They come in any colour. They can be ordered discreetly online. They will be delivered in plain packaging.

They are also called a portable urinal.