Interesting build, similar to what I did for a dust collector for a shop vac. The difference is the intake line seems to go into the water so the ash gets sucked into the water on its way thru. Good way to make sure you don’t suck up any embers into your vac and start a fire in it.
http://www.instructables.com/id/Water-Filter-for-Fireplace-Ash-Vacuum-Cleaner/