Toilets, Sinks, Showers, Tubs and Disposals - Bubbling from toilet and shower drain

When my washer drains, I get bubbles coming up from the nearby toilet. Separately, if I flush that toilet I get a large air bubble from the toilet before it empties. If I then flush that toilet again right away, I get water bubbling up from the adjacent shower drain.

I have no problems/reaction when using any other plumbing in the house - the problem seems confined to the toilet/shower/washer which are all near each other.

I've tried various chemicals to no avail.

Is this a vent problem? The vent is easily accessible on the roof over the bathroom in question. If the vent is the problem, do I just snake a hose down the vent pipe and flush it out?

Thanks.

Don

Don: you don't need us! You have it figured out just fine. You do seem to have a vent problem, and chugging it with a garden hose should remove the clog and allow venting pressure to make the commode and other facilities to drain properly. Right now, they are having to grab air any way they can, thus causing the air bubbles being sucked up the drain pipe. Good luck with it, and be careful on the roof, as falling is fun, but the sudden stop ain't.