A drainage system is provided for draining liquid accidentally spilled on a casing having a plurality of pushbuttons on a surface of the casing. The first correcting filter is configured to reduce a channel impulse response mismatch between the first low pass filter and a second low pass filter, which is configured to attenuate frequencies in a Q-channel of the incoming signal. One screen assembly includes filter mediums supported by a rigid member located exterior to a portion of a base pipe. The first side of the first compartment has an elongated first slot therein.