That’s a good tip for dealing with under-deck wasps, thanks. The way I’ve dealt with under-deck wasps in the past has been with a setup I originally got to deal with carpenter bees that dig deep holes in wood-- a powder insecticide delivered with a bellows-type squeeze thing and a nozzle at the end of a long metal tube. I have to wait until night when they’re dormant and shoot the powder through the gaps in the deck slats. Effective, but it usually takes a few nights to get them all. Your method has the advantage of being non-toxic and being able to keep more of a distance from them.