Chas12 wrote:
I have no idea why people reply to innocent questions in this manner.

I've seen louvered type that will actually close, or a vynal type with
flap
the metal ones stop working after lint gets into the hinges.

tape the wall up and stick the end of the dryer vent hose end down into
a 5 gallon bucket of water, put a brick on it to hold it down in there.
free lint free heat