There is a nice thread on this topic and the thread is titled "Is it possible to Hide implants ?"
Here are my thoughts on the issue (as stated to the person on that thread):
I agree with all the other posters who say that telling lies (or witholding info) is just not a good idea since it destroys trust in the relationship should things move towards a longer term.
However, I can understand that for a a one night stand, or maybe a three night stand, a 29 year old might want to not disclose it
Pre-intercourse:
--I think pumping up can be easily hidden (for example you can do the 25 squeezes while performing oral sex on her).
--if your pump is lower profile (ie coloplast) and is well behind your balls (like mine is) then there is a 75% chance she will not detect it if she is giving you a blow job and playing with your balls (most women are not that skilled at figuring out what is in your sac and what it's supposed to feel like)
During intercourse:
--no problem, it is like a regular dick except "I get harder and last longer" then normal men
--if you go thrusting for thirty minutes, she might wonder what the hell is going on since no other man has had that type of stamina in her experience
After intercourse:
--this will be the problem. You will still be rock hard after orgasm, and that could be a flag to her
--you would need to pull out immediately and roll over, you will need to deflate which can take 30 seconds and might involve you using your hand to squeeze your dick. Thus, the after intercourse cuddle (Which women love) will just not happen. All this being said, if you are skillful, then this can be done
There is also another a good thread on this topic which was directed to user "RichardTheFrog" with the title "Will this really change my life", it address that 29 year old's questions.
Below is a reprint of my answer to froggy:
by TANGERINE ยป Sun Feb 19, 2017 2:45 pm
yes , the implant will change your sex life infinitely for the better. When you enter the bedroom with a woman, you will have 100% confidence that you can perform like the boss and that this might be one of her best love sessions ever. As others have stated, during the "pre-coital safe sex discussion" typical of encounters these days, you might want to say "by the way, I have had some work done down there; it is not something you will really notice, except that I get harder and last longer than most men" and then when she gets a worried look on her face and says, "ummmm, what do you mean ?" You can say, "well, for example, I am one of the few males that can have multiple orgasms " ... and then let the lovemaking begin !