Jake,
The problem with small compessor mounted moisture traps like on the pic above is that the moisture trap is mounted directly to the compressor and as the compressor heats up thorugh normal use, the moisture trap does too,
A moisture trap works on the basis of temperature differential between the "filter" and the air causing the moisture to condense and collect in the trap. Being attached to the compressor, the metal "filter" heats up and there is insufficient temp differential to cause condensation.
You can add a small in-line moisture trap which is isolated from the compressor by a length of air hose. This should help solve the problem.