Help please!

My septic system is giving me the sh!ts, it should be the other way
around, the balance of power is out of whack at my place...!!

OK, I believe I have a standard type septic, concrete tank with an
inlet pipe & an outlet either side of the inspection lid...

Some years ago I had my tank pumped. Things wouldn't go down as we
would hope and we had people coming for dinner. Phew, that sorted
that, but ever since strife of one kind or another...

My current problem is that when there is no-one at home for a few days
the inlet pipe seems to build a new crust/layer which has the impact
of a blockage.
I have borrowed a friends (also a plumber) home made long handled
plunger and with a lift of the lid (IO Inspection) and a push down the
pipe, I am working fine again...

This seems to happen after only 2-3 days of idle time...

I have fixed my outlet pipe recently, it had a bend/minor kink - since
this, the run off is working fine when the inlet is not blocked...I
have no blockage on the outlet side...

The tank was last pumped approx 18 months ago...

I have tried different toilet papers thinking maybe some float better
than others, but I am not sure what I am looking for so maybe I
haven't tried the correct one...

My plumber friend/neighbour is also unsure of my situation...

Any suggestions please