reliable wireless device, no such thing. If it’s really important then you should wire it all the way.
Failing that, I’d consider a supervised connection where if the device has not reported “something” twice in the longest allowable silent period, then you followup.
I use a couple of dry-contact monitors in my ST setup, Aeotec by Aeon Labs ZW097 Dry Contact Sensor, which you could wire to anything including your float sensor, but FYI I don’t recommend it as the sole solution since my monitoring has shown it misses about 1 in 40-50 “on” events. I expect this is because either it is super-sleepy or ST dropped it (to be fair, it could also be the IOT service provider dropping it, but come on, let’s get real).
Combined with my other monitoring, this is good enough for me. But to monitor your septic / whatever, you should add something like a power monitor on the motor and/or do a cycle count. You know it’s supposed to operate 3-4 times a day and that power is within 200-250 watts ((whatever they are) , and if too much time has elapsed since last cycle or power is out of range then notify you. I would use Grovestreams to provide the notification - it can notify you on lack-of-new-data also.
On the other hand, the leak sensor (Everspring St812) in my sump, being used as a high-level monitor, has been 100% in my testing for more than a year, has I think 6foot lead - I’d try to use that for your application. If it corrodes, just get another one or extend the lead with new jacketed wire. The range of these devices has been pretty good. You might have to rainproof the head.