As super trucker said it's probably the float or dirty/worn float needle or seat,allowing valve to leak when eng at rest,pump may also be leaking internally.
Drain tank,buy/install a fuel shutoff valve between tank & pump,for testing connect a pc of hose from valve to carb bypassing fuel pump,let set a few days(valve open) & see if tank still drains into crankcase,if it does,then problem in carb,if gas still in tank,then pump bad/leaking internally.
The lower half of pump body is a right angle casting with arm in it,there are 2 bolts on flange of casting that hold pump to block,you may have to remove flywheel cover or sheetmetal/plastic covers to see bolts,also goto link below & download a service/repair manual for your eng.
After you locate/repair source of leak,change oil & filter(if eng has)DO NOT operate eng the way it is with gas in oil,gas thins & destroys lube property of oil & you'll be looking for a new eng soon.
LEAVE shutoff valve installed in line & turn off after each use in case leak starts again.