To ensure you never have to live through this story again:
If the drain is moving but slow, the blockage might be a buildup of grease, fat, or "scale" (calcified waste) on the pipes. how to unblock a toilet drain outside
Here’s a full, step-by-step guide to (often a soil vent pipe, manhole, or outdoor toilet waste pipe). To ensure you never have to live through
This is the heavy lifting. If the water is standing still, you need to break the dam. you need to break the dam.