Hi Owen,
Your body is pretty good at taking care of itself as long as you ate not abusing it. Fairly often may be a bit too much.
After ejaculating you should feel a sensation like you need to urinate. That is because semen is not the pH that the urethra likes. Urine is the perfect pH, and it serves to clear out the pipe, so to speak.
If you do not urinate afterwards, the semen will become stickier and can cause a bit of blockage. You should be a little more careful with your aim, if you delayed urination. You could end up writing all over the wall of the restroom. That will not make your mom very happy. ;) You may find yourself in this sticky situation by accident if you have had a nocturnal emission. If so, a little rolling around between your fingers will help unstick matters. While on the topic, unless you want your mom to know how often you are masturbating, use tissues and do not do it in the shower. The man stuff has a way of clumping in water and sticking in little globs on the tub surface.
The urethra is a very tricky place to be putting things. It is very easy to get a Urinary Tract Infection from inserting things. Unless a medical professional is doing the inserting, let that tube be a one-way travel. :)