Title: Fill It Up!
By: Serenity
Pairing: Nick/Greg (sort of)
Summary: Written for the live journal masturbation challenge. Missing scene for Down The Drain. I took a few liberties with Grissom's experiment, but hey, it's all in fun!
Disclaimer: Don't own them, not making any money, not working for CBS.

Greg wandered the halls of the CSI building, trying to clear his head of the autopsy he'd stood in on that morning with Grissom. It had unnerved him, thinking of the human body as nothing but meat, and he felt on edge, agitated. He needed something to do, so he decided to find Grissom and see if there was any way he could help with the latest case.

He found the older man in the lab, stirring a foul smelling brew like a modern day wizard. "What are you doing?" he asked, puzzled.

Grissom looked up from the tank containing his concoction, pleased to see his young protégé. "Good. You're here. Fill this up for me, will ya?" he said, tossing a small tub towards him.

Greg caught the tub, his nose wrinkled as he looked at it. "With what?"

Grissom looked at him incredulously. "It's a urine specimen cup, Greg. What do you think?"

Greg shrugged and turned the tub over in his hands. "Okay…." He turned and made his way to the bathroom. This guy gets weirder every day. he thought.

A while later he returned to the lab, filled tub in his hand. He set the tub on the counter in front of his supervisor. Grissom looked down at him, a smirk twitching at his lip. "That took a long time. You may need a prostate exam."

Greg rolled his eyes at him. "My prostate is just fine. I'm not a soda fountain." Grissom reached behind the counter and pulled out a large plastic bucket. "Hopefully you are, 'cause I need a number two as quickly as possible."

Greg eyed him with scepticism and took the bucket. "What is this all about?" Grissom looked down into the odd looking liquid and raised his eyebrows in that 'this is an important experiment' look that he often got.

"The victim's body was found in a sewer. Ambient temperature 80 degrees. The corrosive chemicals caused the body to decompose faster than normal. I want to find out how much faster." He dropped a pig foetus into the mixture. When he realised Greg hadn't moved he shooed him along with a sharp tone. "Today." He poured the urine into the tank.

Greg turned towards the door, bucket in hand. Ok he thought, Grissom's officially lost it. "This is some kind of CSI hazing. Make me appreciate blood and semen more." He shook his head and made his way to the bathroom.

After 30 minutes and a prayer of thanks that he'd eaten fruit the night before, he returned to the lab, finding Grissom eagerly stirring the foetus around the tank like a kid with his first science experiment. "I hope you're happy now." he huffed, handing the bucket over.

Grissom emptied the bucket into the tank. "Thanks Greg. Before you go, there's one more thing." He began to root around in the cupboard under the counter, his muffled voice drifting up from inside. "You said it made you appreciate blood and semen more, yes?"

Greg leaned over the counter to try and catch a glimpse of what Grissom was doing. "Yeah…… Don't tell me you want my blood?"

Grissom stood up quickly, making Greg jump slightly. "Blood, I have." He tossed Greg another tub. Greg looked at Grissom, down to the tub, then back to Grissom. He shook his head wildly. "No way, Grissom. You can't possibly….."

"All sorts of bodily fluids end up down the drain, Greg. I need to recreate the conditions as accurately as I can." On seeing Greg's panicked face, he lowered his voice. "Don't worry, I'm not going to broadcast it to the lab, it stays between us."

Greg shook his head again, holding the tub at arms length like it already contained something toxic. "You can't expect me to do that…. not… not here.

Grissom shot him one of his patented 'I'm your supervisor and you do as I say' looks. "Use the disabled bathroom, you won't be disturbed there." He tapped his watch. "And time is of the essence Greg, so if I could ask you to get on with the job at hand."

Under any other circumstances Greg would have found Grissom's unfortunate choice of words amusing, but all he could feel was the rolling nausea in the pit of his stomach. He couldn't believe he was going to have to jerk off in the middle of work and then give the by-product to his boss! But if Grissom demanded it, there was nothing he could do.

He made his way to the disabled bathroom, which was situated at the other end of the building opposite the computer room, his walk like that of the condemned man walking the green mile. He carried the tub in his fingertips like it burned just to hold it.

He made sure no one was in the hallway before slipping into the bathroom and locking the door behind him, double checking that it really was locked.

"OK, deep breaths Greg. You can do this. You can do this." He set the tub on the sink and shook his hands loose, skipping on the spot like a prize fighter preparing for the ring.

Slowly and carefully, he unzipped his pants, trying to ignore the slight tremble in his hands. His cock remained stubbornly flaccid as he tugged on it, trying to think of anything to forget where he was. Every pornographic image he could think of flashed through his brain, but non of the panting, eager, nubile young women were doing it for him.

"Shit." he groaned, dreading the conversation he was going to be having with Grissom if he didn't perform. He pulled his pants further down his legs and began to roll his balls with his free hand. That felt nice, so he kept doing it. Suddenly, he heard movement outside the door as the handle behind him began to twist with a squeak.

Greg froze in fear, hoping desperately that the door really was locked, otherwise he was about to give one of his colleagues a hell of a show.

He breathed a sigh of relief when the door remained firmly shut. "OK Greg. You're cool." he told himself. "It's now or never. Lets just get this over with." He began to tug at the head of his cock again, but a knock on the door broke his concentration.

"Er……. Yeah?" he called out, squeezing his eyes shut in acute embarrassment. He could hear shifting outside the door. "Sanders, is that you man? You nearly done? I'm dying here, I've just drank, like, six cups of coffee."

Shit, that was Nick's voice! "Just a minute." he shouted, his own voice wavering. "Why are you down at this end of the building anyway?" Good one Greg, get him into conversation, why don't you!

"I'm working on Cath's case, on the computer. I'm too tired to walk all the way to the men's room. I'm telling you man, my back is killing me sitting there all morning. I would kill for a good deep tissue massage."

With that, Greg got a mental flash of his co-worker, naked from the waist up, his toned muscles slick with oil and being kneaded and loosened… and wait… this can't be right. he thought. His cock had begun to twitch in his hand, and he could feel the familiar heat of blood flooding into it. He grew hard within moments. OK, Greg, what the hell is happening to you, you can't get aroused by thinking about every porno you've ever seen, but your (very male) co worker is making you hot? Just by talking to you?

Nick continued chatting, unaware of his effect on the young CSI. "I can't wait to just get home, get out of these clothes and take a long, hot shower, man." Greg's hand sped up as he thought of Nick, naked and wet and soaping himself all over. "Yeah, me too Nick." he said, his voice hitching as his thumb ran over the flushed head, sweeping a pearl of precum across the tip. His other hand grasped at his balls, rolling them in his fingers, noticing how full and heavy they suddenly felt. He let out a moan, a little louder than he intended.

"Are you OK in there Greg? You sound a little distracted." Nick inquired, his voice a strange mixture of humour and concern. "Do you need a hand with anything?"

And oh fuck, if that wasn't the worst and best thing Nick could say. Images flooded his mind, fantasies of Nick entering the bathroom, that shit eating grin on his face, and replacing Greg's hand with his own . He could almost feel Nick standing behind him, working his throbbing erection like it was his own, running his thumb over the ridge with every brush of his hand.

He blindly groped for the faucet and turned the cold water on full blast to try and disguise the sticky slap slapping sound of skin on skin. Nick continued to talk, Greg unable to comprehend any actual words now, just absorbing that sexy Texan drawl as it permeated through the bathroom door and enveloped him.

His faced burned with arousal, his hand at lightening speed now. He couldn't stop the low, throaty moans escaping as he thrust into his hand. Nick's mouth he thought disjointedly, imagining Nick on his knees in front of him, his mouth warm, wet and willing, his tongue twisting around the swollen head.

The tingling in the base of his spine warned him that his orgasm was rapidly approaching, his balls hitching and tightening. He was so close that he almost forgot the purpose of the exercise and only remembered to grab the tub at the very last second, spilling five sharp bursts of hot cream into it.

"Fuck!" he exclaimed as he came, the word echoing around the tiled bathroom. He gasped with ragged breaths as the sensations ebbed away, leaving him blissfully calm for a moment. His moment didn't last long. He jumped as another sharp tap sounded on the door. "Greg, are you sure you're OK? If you're not, I can break the door down……"

"No!" Greg yelled a little too quickly. "I'm fine, honestly, I'll be out it a second!" He twisted the lid back on the tub and washed his hands at the sink, checking his reflection in the mirror. His face was bright red and his eyes had a glazed over look, a telling sign of what he'd just done.

Shrugging and hoping no one would notice, he tucked the tub into the waistband of his jeans and pulled his shirt over the top to hide the bump. Taking a deep breath, he opened the door where Nick was now almost dancing trying to hold on to the contents of his bladder.

"Dammit Greg, what the hell were you doing in there, jerking off?" He asked rhetorically as he pushed past him and slammed the door behind him in his haste.

Greg could only smile as he made his way back to the lab. Perhaps this CSI hazing had it's perks after all.