I use a Marlin 30Fr curved catheter; it is easier on the valve than a catheter with an opening up front. Several postings mention use of a 24Fr catheter to open a difficult valve. I have found that by sitting bold upright on the toilet seat and then concentrating on completely relaxing the abdominal muscles in the stoma area (think “let it drop down”) usually brings results. Sometime, I have to make several attempts, but I have always gotten in. Never try to force the catheter in. I have never had to use the smaller 24Fr catheter. Remember: RELAX.