map transition without carrying over props?

I’m working on a mod with some friends: Wolfenstein source, ( before anyone compains this isn’t relevant to GMOD, I am planning to make a GMOD addon pack ( models/maps/etc ) once the mod is finished! )

And we’re having a big problem with level transitions, when we transition a level, lots of props, and other stuff are being carried over from the previous level, is there a way to stop this? Or a workaround that you guys could suggest?

Firstly, it doesn’t have to be relevant to GMod, it just has to be .bsp format.

Perhaps on the trigger that starts the level transition, have it “kill” all the props that are being carried over.

Valve included the VMFs for the first few trainstation maps. Look at those and you’ll see how they did it.