Can be tucked nicely into the floor or corner of a base.
This ues a 0 tick glitch where one dispenser dispenses water at the same time another dispenser sucks it back, all in the same tick. This causes the cauldron below to update, and because of the dripstone and lava above, it fills with lava.
You could get rid of the piston tape and have just the moving dispensers, but that's boring.