Flushing out a tankless water heater to clean and descale

My first time doing a descaling flush to clean out my tankless water heater. This is an annual maintenance you should do if you own one of these water heaters.

Supplies used:
Pump: http://a.co/fUnr2g6
Hoses: http://a.co/d7Fiurm
Bucket: any bucket
Distilled White Vinegar (5% acidity)