Biological issues of the Quarians

So I recently saw this particular joke on a review for a fan fiction. If you've played Mass Effect you will probably laugh as hard as I did.

"So a krogan, turian, quarian and human walk into an elevator and they're just standing there, awkwardly quiet. In the back the human gestures to the turian next to him they both notice an oddly growing lump in the back of the female quarian's enviro suit. A small tube is released and extends towards the krogan and retracts, the lump is gone... The smell hits them.
Krogan, "Whoops, how'd that slip out?"
The elevator stops and the quarian quickly scampers out after the krogan. All the turian and human can do is stare at each other.
Turian,"Well. I guess that answers the age old question about quarians." and steps off.
Leaving the poor human to wish he'd never left his bed."

For those who haven't played Mass Effect, Quarians live on what is known as the Migrant Fleet after they were forced off of their home world. When they leave the fleet they have to wear environmental suits to survive due to a non-existent immune system.