l have a Reinell boat 165 horse power inboard/outboard motor.When l hook up water to it with the hose and start the boat l notice a black substance mixed with the water coming out on the ground... is this normal.And if not what is it?Also when the boat is on the lake where is the intake for the water?Is it the square part above the propeller or is it with the propeller?There are no small holes like on some boats where the water intake is... thanks
The drive is OMC

What make drive do u have???? Is it an OMC? l say that because it has a water hose connecting on the upper housing pivit arm. The black stuff might be just normal gunk, from rust & stuff in the exhaust manifolds, including burned fuel & oil, However, check the engine oil level dipstick & the outdrive levels, One on top, dip stick & the other on the side above the cavitation plate, large screw. The water pick up is on the front of the exhaust housing above & behind the prop. It loks like screen wire.

It is not uncommon to have unburned engine oil dripping from the exhaust of a 2-stroke marine engine that is been sitting idle for awhile, or been run mostly at low speeds. Especially a carbed motor.

Might want to check the gear oil for water intrusion.

that is just carbon from the exhaust - you could go to the touble of decoking - but genrally servicing and running hard(ish) will do the trick of keeping it clean.
The water intake will not be through the prop but may be the square hole - but where ever it is it will be on the side of the leg not the back,

l have seen that before and it is normally carbon left in the exhaust. You are just washing it out.