Not sure about siphon because i don't use it. I just do the water changes without that. But when you do water change you need to rinse the filter
To do this, first you want to get a container and put some tank water in it. (NEVER use tap or new water as this will kill your marvelous bacteria colony you have waited so patiently to grow.) Remove the air line and tubing from the sponge. Place the sponge in the container of tank water and gently squeeze a few times. Replace the tube and air line and reset into tank.
And when you do full water change you need to acclimate your betta to the new water to make sure you don't shock him with the temp difference.
Do you need instructions on acclimation?