I've seen those vacuum reserve tanks on Prefects do their job very nicely, thank you! Probably 20 years ago now, my then-brother-in-law had a very nice Prefect, in which the wipers did seem to keep going in situations that would've brought the wipers on my '51 Chevrolet to a halt!
I didn't know about the vacuum reserve tank until he showed it to me. At that moment, I was struck by the fact that it (a Trico part as I recall) bore a most striking resemblance to a vacuum tank I remembered on my mom's old '68 Ford LTD Country Squire! On that car, it served as a reserve tank for the vacuum-operated headlight doors.