No it's not urine. Nor, is it beer. 

Although, the contents of the bag did come out of my body (and were subsequently put back in). 

The yellow liquid in the bag is a pint of my plasma and platelets, siphoned and re-injected into my veins via an Apheresis apparatus at my thrice-annual blood donation. I donate two pints at a time so I can only give once every four months. I give two, and they give me my plasma and platelets back. It's a tingly feeling.  

Read: The Friendliest Vampires I Know 

I often use my Patch platform to spout off about the virtues of giving the gift of life at your local American Red Cross donation center. Fortunately, for the fine residents of Timonium the American Red Cross is in our backyards.

You should schedule a donation as soon as you can. There is currently a critical need for donors with a Type O blood. 

"Approximately 48 percent of the population in the United States has Type O blood," reads a statement on the American Red Cross website. "There must always be enough Type O blood on hand to meet their needs, as well as the needs of patients who may receive Type O in an emergency. Type O Negative blood is considered universal and can be transfused to anyone in emergency situations when doctors don’t have time to get the patient’s blood type."

Click here to find out if you're eligible to donate.