I have never heard this before. It sounds like a load of you-know-what. If you think he's cheating - do you have proof? Has something happened to make you think so? Why not just confront him, assuming you have proof, rather than relying on some obscure thing that doesn't even make any logical sense?
That would have to go on my "most ridiculous things heard" list.
First, the penis doesn't fill with semen, the testicles do. The only time the penis fills with semen is while he's ejaculating. And even if it were the penis that held the semen reserve (which it doesn't), who's to say he isn't masturbating? Would bath water know the difference between semen released from masturbation vs. sex with a partner? Nope.
A FLOATING PENIS IN THE BATH TUB DON'T MEAN HE'S CHEATING... mine floats if I bath but I take showers and I don't cheat!!
besides if a penis has semen in it it would still float...heck ain't you ever floated in a swimming pool..your arms legs are a lot heavier than a penis and they float.
MAYBE THE ONLY THING THAT COULD GET YOUR CURIOUSITY UP IS IF HIS PENIS STAYS RED ALL THE TIME AND YOU DON'T HAVE SEX WITH HIM FOR A FEW DAYS??, THEN YEAH THAT MIGHT RAISE SOME QUESTION, BUT EVEN THAT DON'T MEAN HE'S CHEATING.....HE CAN ALWAYS SAY ITS JUST HIM SCRACHING IT, OR MAYBE THE LAUNDRY DETER IS IRRATING IT .
OR MAYBE HE SMELLS FISHY??
Thats some old wives tale that somebody somewhere probably actually believes. Yes what all these other guys have stated, ''the penis does not hold semen''. Hire yourself a PI or something and get this off your mind, it sounds like it's eat on you till your clutching at straws.