You could try the ice trick. I myself have not had to do this because my TT is brand new.
But if your unit does not have a tank flush on it. You could try a back flushing unit.
I bought one called the flush king. From what I can see it works well.
Now I am a bit picky about things. So even after we have been dry camping. I will book a night at a full hook up site and then dump my tank there and do my back flush.
I have done this every time. So from what I can see my tank is coming out nice and clean. It has the clear tube so you know when things are clean.
Also I swaped to rv toilet paper. I did the test and my home paper did pass the break down test. But after using the flush king I found the home paper did nont break down as good or fast as the rv stuff. But please use what you feel comfortable with.