When I flush my toilet, the water continues to drain out until the level is very low and there is a loud glugging noise (presumably due to air getting in because the water is so low).
This gradually refills so that the next time I use the toilet, the water level is normal.
The toilet cistern is built in so not an easy job to open it up to have a look at what might be going on.
Any ideas what is going on and what can be done?