Well I'll just jump into this and say all our drains are flowing slowly- sinks, showers, washing machine, toilets. When we shower, our toilets burp. When you flush the toilet, water comes up the sink in the bathroom. The toilets also burp during the day. When you come home, the water in the toilets is almost all gone. I suspect the main is partially blocked. at a previous house, there was a "Y" pipe with a cap on one end where the main exited the house, but this home was built in the 1940's and we have no such luck here. Is a visit from my friendly neighborhood rooter guy in order? (One lives two house over on the the other side of the alley). Anything I can try first? Thanks in advance.

speedball1

You just may have two problems. A partial blockage in the main that's causing the backup in the sink and a blocked vent that's pulling the water out of your toilet bowl by suction caused be the toilet attempting the system.
A blocked vent would also cause your drains to drain slowly while a partial clog would cause the discharge to hit the clog, bounce back sending a bubble of air ahead of it causing a belch or a burp. The answer is to snake out both lines. Good luck, Tom