We are having intermittent trouble with the drains in our main bathroom. The initial culprit seems to be the toilet. When flushed, it will fill like it is clogged, then slowly drain out until it is almost empty and the water level is well below where it should be. It accompanies this with a lot of burping, which occurs even when the toilet is not being flushed, or even being used. Plunging the toilet will occasionally help the situation to a degree, but plunging the toilet causes the sink nearby to bubble and burp, and vice versa. After a few days of this kind of trouble, it will stop and the toilet will work normally for weeks or months until it happens again. We have noticed that frequently a period of rain seems to trigger this event, but not always, and it will sometimes happen when it hasn't been raining. Any advice would be greatly appreciated. I'm hoping very much that we don't have to call a plumber in on this, since money is tight these days. Thank you!

Its quite possible someone flushed something that has partially clogged your drain..

I had this happen to me once. someone flushed a kitchen paper down there, it cloged the main waste sack. a plumber came. started plunging away like a mad man. you don't want to know what came out from the walk in shower drains...

To make a long story short. he had to use one of those very very very long drain snakes. that run on a motor. sent it in. pulled it out. it was the kitchen paper. not even slightly decomposed... since your toilet still drains. I wonder if it would be useful to send in a liquid plumbing agent...