We're using a 1.5" peristaltic pump to empty a vertical container in a smooth and stable rate (around 30L/min).
What we noticed is a repeatable distortion in the flow rate caused by the peristaltic tube volume change due to the pump.
Roller engagement, causing momentary back flow. This phenomena is highly unwanted by us since it causes a pulsing  flow pattern.
We're looking for a solution for that.

Mike Halloran is right. A peristaltic pump is a rotating positive displacement pump but creates pulsations like an oscillating PD pump. Oscillating PD pumps usually come along with an appropiately sizes pulsation dampener but I have never seens this as standard for a peristaltic pump. A pulsation dampener (air over liquid or bladder type) will solve that problem if correctly sized. 

All the dampeners based solutions are based on pressure rise and air cushion device volume compensation. In my case the pressure is very low, between 4m to 0.5m (12 to 2 ft) water height head. There is no bladder or diaphragm dampener designed for such low pressure. Also the dampeners are providing partial solution only.

Use a multi-cavity (triplex) piston/plunger/diaphragm pump.

Along the same principle as triplex and other multi-cavity pumps, try ganging three or more peristaltics together, with the cam lobes timed 360/n/3 degrees apart (n = number of cam lobes).  If you must stay with peristaltics.

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