Okay, it's pus. And I only corrected because your Subject line reading PUSS, coupled with where the licking is occurring, made me laugh.
Are you sure it's pus? It might be some seminal fluid, in which case, it's completely okay. He'll.... uh.... take care of it himself (how old is he)? If it's very thick, smelly, and has a greenish/yellow tinge, it might be discharge from a UTI. A trip to the vet might be in order.
Dan, leave this thread now, I'm about to use the word you hate.
What you're prolly seeing is smegma (aka: man goo). Smegma is the normal sloughing of cells and accumulation of debris. Its (whitish color is normal) unless you see a greenish discharge then you need to see a vet. Some dogs are better at keeping themselves cleaner than others.