Tubing may be too long. Any loop in the pipe will cause urine to backup, loosening the seal of the sheath. Adjust the length by measuring against the leg and cutting out a section of the tubing above the bag.
Use a plastic connector purchased from any hardware to re-join the tube, ensuring the pipe is the right length for the leg and exits trousers just below the shoe/footplate. When making up a new leg bag don’t forget to rescue the plastic connector and clean it.
At some point, you will not be able to empty your leg bag yourself. A friend may help but if going out for long periods by yourself, simply leave home with the tap turned on.
To void, drive to the toilet/urinal. Wait until there are absolutely no drips, before driving off. Using this method gives complete independence. NB. An off-cut from the bag tubing can be used to lengthen the tube below the tap.