This didn't just happen, Sounds like it has been building up,.....maybe since new, draining off nothing but the water, while the solid was building up, and getting dryer all the time to where it is now a solid block. You need to just slowly break it up w/ a full flow water hose, from the bottom first, and if no good, do it from the top. One thing about it, if you are the normal, you'll get it, one way or another, and you'll never let it happen again.
I had it happen once in 45 yrs.
Rich
'01 31' Rexall Vision, Generac 5.5k, 1000 watt Honda, PD 9245 conv, 300 watts Solar, 150 watt inv, 2 Cos 6v batts, ammeters, led voltmeters all over the place, KD/sat, 2 Oly Cat heaters w/ ox, and towing a 2012 Liberty, Lowe bass boat, or a Kawi Mule.