Washcloth is Towelie and Rebecca's son. Washcloth makes his first and only appearance in the episode, "Crippled Summer".
Background
During a brief period in which Towelie managed to get clean of drugs, he entered in a loving relationship with a woman named Rebecca. Although they never married, soon after their relationship started, Rebecca (through unknown means) became pregnant and soon gave birth to Washcloth. Unlike Towelie, Washcloth does not appear to be as physically developed (he has no eyes, mouth, arms or legs), but he apparently is able to convey his feelings.
Unfortunately, soon after his birth, Towelie's past addiction to weed gave birth to other addictions including cocaine and meth. His addiction soon became so bad that Rebecca had no choice but to throw out Towelie, feeling that he would be a bad influence on their son.
Towelie would often call Rebecca while high, demanding that he be allowed to talk to Washcloth, each time with Rebecca refusing. When the boys also reached their limits in regards to dealing with Towelie's drug problem, they set up an intervention for him. Butters managed to apparently convince Rebecca to allow him to take Washcloth (who was upset by Towelie getting high and abusive) to the intervention. Upon seeing his son for the first time in months, Towelie then promised that he would never leave or upset his son again and agreed to go into rehab. Towelie has since then gotten clean and moved back in with Rebecca and Washcloth.
Appearance
He appears as a regular, blue-green washcloth, strangely lacking facial features.