The desire to breed him overtakes you, and with your knees loudly thudding onto the floor, you alert Davis to what you're doing, startling him and making a massive load of shit splorch out from his hole over your crotch, coating your beast briefs and cock in shit before you line it up to his donut. "W-Wait! Get the diaper fir- ARF!" He yelps, your massive pole of a dick spearing him deeply. The waves of shit stop, and you feel an incredible wave of pure pleasure and disgusting taboo realizations make you shudder in ecstasy. The big fat boof looks incredibly happy, panting and drooling as much as a real mutt. Precum quickly shoots into him, and you can feel his hole clamping down tight on your cock. His belly slowly grows as you stop his flow of poop dumping, and you take this time to relieve yourself as you stuff your cock in balls deep inside the saint bernard man in front of you.
With a slow, deep groan, you feel your own donut open up and spread outward. A massive, completely solid turd steams outwards from your hole, tenting your beast briefs behind you and beginning to coil as you feel the hot mess pile up quickly. Your dump grows and grows, eventually steaming against the back of your huge sack as you feel it all bloat your diaper. The mess quickly spreads further, coating all of your ass meat and soon enveloping your bull nuts. With a moan of pure pleasure, you draw your attention back forward to look at the hot, disgustingly raunchy ass you're plowing. A pool of pre, shit, and sweat grows underneath you both, and Davis' head is rested on the ground, his ass pointed up for you to fuck and his tail wagging wildly. Although, you also notice that his belly is deflating, and a bizarrely warm sensation rushed through your cock... and then your balls!?
After a few moments of heavy breathing and drooling, you realize that your cock being stuffed into Davis' eternally-pooping butthole means the only way out is into your cock! The feeling of your urethra spreading open, without pain, is the most bizarre but pleasing feeling you can imagine. Your cock looks bloated and knobbly, with every hard canine turd flowing backwards in your precum-stream down to your balls, filling them both up as if it were always meant to be. Your thick seed mixes with the turds, soaking into them and making them bloat full of your cream, and the sensation just makes your balls slightly squishier, with the well-known dark-brown color tinting them from the outside. As you continue to fart and shit in your own diaper, you slowly get into a rhythm with Davis, thrusting forward into his ass as he poops directly into your sack. "I've never... p-pooped in a c-COCK befORE!" The saint bernard moans and gasps, the pleasure seemingly just as good for him. "Fuck me... h-harder!" He begs of you, farting around your cock with every thrust. Your meaty paws grip onto his thick hips, pulling his ass against your thrusts as he moves with you to hump him harder.
You continue thrusting in bliss, farting, shitting, even belching as your balls inflate further and further with dog shit.