I want to catheterize triple lumen catheter to let out all of the urine and insert synthetic urine for a drug test, any comments?

Serious answer: As you know, try your best to not use illegal drugs. Seek help if needed 2nd, you sound like you are going to insert the catheter yourself ; i would assume in a nonsterile way. You will increase your chance of getting an infection in your urethra and/or bladder. Not a fun place for any infection. There could also be possible legal ramifications, talk to a lawyer. Bad idea, dont compound one probl.

Not a good idea: Urine is made continuously. So trying to put a substitute for your urine won't hide prior drug use. There are risks of self catheterization. You could tear your urethra or introduce an infection into your bladder. This is besides that this would mean cheating on a drug test which could be illegal depending on what agency you are trying to cheat. I cannot support this and recommend it.