The earlier thing with the weapon, using toggleeventenabled I find better to use.
Ok, the gas.
According to you description, I understood that you want to know how to change the color of bricks from black (gas) to clear (no gas). Idk by what means you will be emptying the container, but my example will use two bricks; a large brick call Gascontainer, an a small one name Gasemptier.
Here is the chain of events on the Gasemptier
[/] 0 onactivate->named brick=Gascanister->setcolor->clear
[/] 5000 onactivate->named brick=Gascanister->set color->black
More can be done if you want it to be a liquid in a glass container.
And through all my years of BL, I have never changed the item spawn time from 4, I have never found a reason to.