Some things By "Other side from drain" Drain is normally on Driver's side of RV. Toilet in this case is on Curb side. That's simple
Sensor shows 2/3 full.. Working or rather not working as designed the sensors are .. Well let's just say the black tank is where they belong. Mine are like that too it is next to impossible to get 'em to work properly
Two suggestions one of which I hope to try some day
1: Horst Miracle probes.. They CLAIM they will work I've read good reports but have yet to try
1: See Level. Again I've not used it but since the technology is different it WILL work.