I hope I am interpreting this correctly, because gods do I love this. Much like I enjoy inflation in general, come inflation in someone’s bladder is… a guilty pleasure of mine(same with come inflation in someone’s balls no matter how unrealistic)
So Geralt is pent up and complaining about it, Jaskier telling him he’s exaggerating and ignoring it. So Geralt decides to show him just how bad it can be being pent up with so much thick, sticky come inside and ties the bard up. He works the sound inside slowly, careful with Jaskier yet smiling at his eager moans. It’s hollow and long, perfectly shaped to go all the way into the man’s bladder and open him up for the witcher. After breaching the sphincter he watches as Jaskier loses control and empties his bladder into the chamberpot, Geralt nice enough to not soil the bedsheets.
By then Geralt is so hard he can’t keep from touching himself, sighing and grunting as he jacks himself off. Jaskier is speared open before him, his most precious place stretched and ready to be filled by him. When he feels his balls draw up he kneels just before the bard, aiming his slit right at the hollow sound and lets go. Jaskier is immediately catching on and I think he freaks out just a little at first, squirming as he can feel the hot seed travel down the cold, metal tube and then pooling inside of his bladder. And it’s so much, much more than what the witcher normally produces and what would dwarf anyone’s volume. By the time Geralt is done Jaskier is sure he’s filled to the brim with the thick come, too sticky and viscous to leak back out of his hard cock the way his piss did.
But Geralt has no intention to stop just yet. His balls are filled with the stuff and aching with need to get it out, so he keeps stroking himself. When Jaskier protests he tells him it’s all to trach him a lesson, to make sure he knows how bad it is for a witcher to stay pent up and that he is in fact not exaggerating. He can see it’s uncomfortable, but the constant scent of lust coming off the man tells him it’s all okay. So he shoots another lod down the shaft, and a third. It takes several minutes to make it all flow down into the tube, it sticking to the surface and going down in thick globs.
By then Jaskier’s bladder is bulging, making a small dent in his otherwise flat stomach and Geralt smiles as he leans down to inspect it. He smells so much like him, claimed by Geralt from all directions, and it’s intoxicating. He is careful as he pulls the sound out, can tell just how badly filled Jaskier is from the way his belly cramps up trying to expel the liquid. But it doesn’t work, the bard panicking as he can’t get it out. It’s stuck, clinging to the tight walls and refusing to move anywhere, barely escaping the sphincter and travelling torturously slowly down his urethra.
Geralt asks him if he aches, if it’s too much pressure. He asks Jaskier to imagine all of that inside his balls, filling up in his sac and prostate trying to escape but not being allowed to. He starts pumping his shaft slowly, coaxing more of the fluid to seep out, bubbling out of his slit and dragging more along. It’s stringy and gooey, Jaskier almost sure he could start pulling on the small amount dripping out of him and would be able to pull more out just from that. But each time Geralt pumps his cock, it pulls more along, seeping out like sap.
The witcher presses down on his bladder and the pressure is too much for him, the thick seed trying to make space while sticking to his insides and desperately trying to escape. It’s packed into his urethra so much that it can’t escape any faster, just a long torturous experience as the man forces more out of him slowly, slowly.