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my name is Billy.
The easiest way is with a shop vacuum. That way it is just a matter of removing one tube or hose and applying suction.
The alternative is to unhook all piping, remove and wash out. The shop vacuum is much easier.
I have done that unit both ways...
direct from drain end point and also from the cold header box.
Do you mean you are hard piped pvc and just do not want to cut it?
The ml193 just has a basic external trap box
look at 33 and 34 HERE for the various configurations
Worst case is cut pvc and vacuum and put back together a pvc fitting..less than $3 fix.
You can also come from the furnace side via threaded fitting...
And the most basic....just apply suction at the drain pipe end point...that purges the trap also.
And the majority of traps have a clean out cap.
See page 39 in ml193 manual HERE