that is a helluva guess (A Tee in the Pressure Line)
Putting a Tee into the pressure line is a pretty basic mistake. I think we've all done it. Doesn't work.
What happens is that the hydrualic fluid just takes the path of least resistance - which in this case is whichever return line looks most favorable. The fluid returns back to the sump, and never gets around to doing any work.
There is a trick for making Tee connection in a pressure line - and I'm sure that Harry knows this one too. It was commonly done on old Massey Fergusons from the 40s and 50s when people wanted to run a loader and still have 3pt capability.
The trick is that instead of a Tee, you use a manual hydraulic selector valve. The manual selector valve has a hand lever on it that will only let you send pressure to one system at a time.
Here's how it works on a tractor: Most people mount the selector valve on the dash for convenience. You can turn the lever on the selector valve one way to pressurize the 3pt system, raise us the implement, close off the 3pt hold-in-place valve (usually between your feet) and now the 3pt implement is held up & out of the way.
So you reach forward and switch the selector valve over to pressurize the loader and you can use the front end loader for as long as you like....or until you need to shift back to the 3pt. ....and repeat.....
This constant switching can be quite a circus given an old Massy with a pathetic 3 gal/minute hydraullic flow and leaky hydraulics at both ends. But it works. And lots of old farm tractors were rigged that way. It's cheap and easy and any front end loader is a wonderful thing.
I mention it not because it is the best way to do it, but because so many were done that way.
The path that Harry has you on to use the power beyond port is much, much better.
Oh, and DO NOT use plumbing fittings. Use hydraulic fittings. Plumbing fittings will break and spray.
rScotty