In article .com,
wrote:

In this discussion there are some reports about auto-wattering from
water butts using timer. But I did not find exact type which work
or does not work.
I have water butts 1 meter above land - it is 0,1 bar pressure.

Please, have somebody type:

Hozelock AC4 - works it or not?

Claber Video 2 - works it or not?

Gardena T/C/WT 1030 - works it or not?

You would need 1 bar pressure to make a timer work with a water butt.
Your best bet would be to drop a submersible pump into the butt (eg
Hozelock Water Butt Pump) and put a plug timer on the power point so
that the pump comes on at the required times. Your drip system (my
assumption) would be connected to the pump.

If your drippers are not of the pressure-compensating type then you
will also need to install an air gap to prevent siphoning from the
pump. Easily done with a length of 4mm micro hose T-joined to the
supply hose at its highest point above the max water level in the butt.