RV Waste tanks have roof top vents....no pressure build up unless vents are blocked
Have done the extra valve on past 3 trailers for over 15 yrs.
I have not had any issues.
I have not had any backup problems
AND I don't even pay any attention to the tank level monitors.
I do know/understand how my waste tanks function/are plumbed and how long I can go before needing to dump.
'old adage'
When toilet burps...time to dump
When sink/shower start to drain slower....time to dump
When water pump goes burrrrup...need more water
YMMV......