Sometimes when I pull the catheter out, the membrane is stuck to the side of the tube
This condition will ONLY happen if you break the lock with the cervix. This is why we teach you to put forward pressure against the vulva prior to squeezing, and also not to pull up on the catheter when letting the air in the tube flow up into the bottle. When this happens you will get a lot of back flow too, and you should re-service the animal. This is strictly operator error and is very uncommon after the first couple days of using the product.