Pulling out a urethral Foley is a very, very bad idea. Even if the Foley balloon is not fully deflated prior to removal it can hurt like hell.
Several things:
First off, a urinary catheter is MUCH bigger in relation to the size of the passage than a rectal balloon catheter. A rectal catheter of the same proportions would be more that softball size.
If the catheter was recently inserted using an anesthetic gel, be extra careful. The gel deadens pain and masks possible damage.
Do not cut off the valve to deflate the balloon. It is possible for the balloon to fold back and block the exit port. In such a case the balloon will need to be partly re-inflated and you can't do that if the valve is cut off.
For similar reasons, do not pull on the syringe when deflating the catheter. Just insert the syringe tip into the valve and relax.
The syringe should gently fill with all the water originally injected. A tiny tug at the very start may be needed to unstick the piston.
When the balloon is empty the catheter usually will start to slide out slowly, without pulling, of it's own accord. I find that sliding out naturally is the most comfortable way of removal. It may take a few minutes and is usually followed by a squirt of pee. Hospital nurses don't usually do this, but IMO it's better.
If the catheter doesn't come out easily, seek real medical help. Wearing diapers when you want can be fun, but needing to for life is another matter.