Don't do it as a get rich quick scheme, but as a ditch digger by trade , you might.
The reason old outhouse/privy locations yield hidden treasures is because glass and other old items were dumped in them many years ago like a mini land fill.
Garbage/ glass from back then if intact (bottles ect.) in many instances has value.
They make detectors that can be submerged, I've used a Tesero Tiger Shark that really does well IMO, good for diving.