With a squirting dildo

Caitlin tells you: "Open the drawer on my nightstand! It has something that can help us save some of your sperm for me!" You open the drawer and find a large dildo which closely matches your own penis. You wonder how that's going to help you, but as you take the dildo from the drawer, you notice it has a ball-shaped reservoir at the bottom, like a weird single testicle. You hand the dildo to Caitlin, who grabs the bulb at the base of the dildo and squeezes it hard. She then inserts the tip of the dildo into her cleavage and slowly releases the pressure on the bulb. With a slurping noise, it sucks some of your cum into the reservoir. You realize it's one of the novelty dildos that can be filled with a liquid and squirted out by squeezing the bulb. Caitlin repeats this a couple of times, careful not to squeeze out any of the salvaged sperm. You watch Caitlin vacuum most of the mess on her boobs into the dildo like a literal backwards cumshot.

"There", Caitlin says, "should be enough of it in there. Maybe add a little something for additional pressure..."

Caitlin opens another drawer on her nightstand and pulls out a clear plastic bottle with a wide top. The label reads "Porn Star Cum" and it is half filled with a sticky white goo. You realize it is the same kind of fake cum used as a prop in porn shoots. Caitlin screws open the bottle and inserts the tip of her squirting dildo into the bottle and slurps in a generous helping of the fake cum.

"Ahhh.... there we go! Now I feel like we're going to be able to do fertilizing", she says, sliding the dildo into her pussy. She begins to fuck herself, using your cum infused dildo. After a while, she pauses and lets go of the dildo, leaving it sticking out of her pussy with the mono-testicle pointing at you.

"I need to have my fun as well. But maybe you'll want to do the honors?", she asks you with a seductive smile. Although you didn't plan this, this is pretty hot. You grab hold of the dildo and start moving the dildo. Caitlin starts panting, "I meant spray the load inside, not this! But it feels so damn good, just keep going..."

You keep eye contact with her as you pump the dildo in and out of her pussy. You notice she's nearing her peak and decide that this is a good time to release your salvaged load.

"Here it... COMES!" you shout and squeeze the bulb on the dildo, and hear a very lewd sounding spurting noise as the dildo empties its contents inside Caitlin. At Caitlin realizes what is happening, she starts to pant heavily.

"Ohhh yesss.... that's it...... keep going...... make me cum... make me cum...", she says in between heavy panting.

You pump the dildo in and out of her, making loud splurting noises as it travels up and down her cum filled vagina.

"Ahh... AHAH... OHHHH..... Yessss...... THAT'S IT..... FUCK ME..... FUCK ME...... CUMMING..." she pants.

Caitlin arches her back on the bed and you carry on fucking her as she orgasms for what seems like an eternity. You then stop and pull out the dildo. You look at what is in front of you: Your girlfriend's sister, her G cup breasts stained with your cum, with a mixture of fake and real cum trickling out of her crotch. You feel your cock stirring back to life.