Every now and then dirty, black water backs up from my shower drain and sits still for a few hours and then drains back out, the toilet in the same bathroom also sometimes has no water in the bowl.
Yesterday the sink in my other bathroom was clogged and I tried Drano but the water did not even move. This morning I noticed the shower in the other bathroom backed up again with dirty, standing water. Are these problems related? I am going to call a plumber but wanted to know if this is serious.
Thanks for your help!

Hey JR,

While the problems may not be related they are certainly in the same system, the drainage and venting system. You have blockages in both the house vents and drains. Your plumber should snake the vents in both bathrooms and also the bathroom drains. Every fixture that backs up has a clog located downstream from it. Sounds like the plumber has his work cut out for him.
Good luck, Tom