We have a pump out toilet on our narrowboat. It is a flush toilet not a dump through. We have pumped it out several times without any problems, however this week we pumped it out when the indicator light went red (we knew it was due as we log how many flushes) later that day it showed red again & the flush water did not go down. We are leisure users & the last time we pumped out was October 2020, as due to lockdowns & maintenance work etc we've not been able to use the boat.
Any advice gratefully received:
Is this something we can sort ourselves or do we need to get professional help?