Bathtub and toilet drains slow, toilet bubbles?

Could be. You speak as if you have had venting problems before with this.

Check the vent to be sure, which you will probably have to get on the roof and snake it too. Could be bee's, wasp, bird, anything. Is this the only bathroom doing this? The way the whole bathroom is all draining slow leads me to believe that it won't be just the toilet or just the bathtub drain that is the problem. It will be further down the line than that.

They make a way, way better product than Drano. Simply called drain opener by Floweasy. I can tell you, if there is something in your lines, it will be taken care of by that stuff.

It sounds to me like a ventilation problem. The fact that your toilet bubbles, and you have to have a certain volume of water, for it to drain, are good indicators of this. The volume of water is needed to overcome the vacuum imposed by not having enough ventilation. The bubbles are from air having been sucked down the drain, and it is now escaping.

There may still be a blockage, or other restriction in the flow, too. Check the fall of the drain line(s), and even any bends in the line. Is there a 'hard 90', or 'soft 90' elbow in place where the drain line needs to bend?

I'd recommend having a couple of plumbers out to check out the system, and give you some recommendations on what needs to be done.

Good Luck

No, paper doesn't go through the vent stack (only air goes through the vent). The vent works by allowing air into the pipe when the water drains (like the small vent hole on a gas can). If the vent is plugged it causes a vacuum and has to suck air through the water from one of the fixtures (toilet). It's like putting a 5 gallon jug on a water cooler, there isn't a vent hole so the air is sucked through the only opening. The only way I have seen a vent get plugged, is because it was installed wrong and rain water from the vent opening on the roof plugged it. The vent going up to the roof can't have any dips or loops for the rain water to get trapped in. Look up in your attic and make sure they didn't make any funny bends or loops to get around obstacles, causing rain water not to run down into the drain pipe. As far as the water leaking in the wall , you have a leaking pipe and better fix it ASAP or you will have a moldy mess on your hands.