I have a 2073 with a 2075 head unit. I do 50% changes 3 times a week on my 90G Discus tank. I went thru my share of headaches with this filter, but I don't have any issues now.
Couple points that get it to work for me:
1) I never let the water get below the intake basket (which is about 55% of my tank).
2) when I clean the filter, I close off the hose valve, BUT make sure I leave water in the intake hose. I remove the filter and put a bucket under the hoses for any drips....
3) I clean & re install the filter (empty) and refill the tank to the top, I turn off the water, but leave the refill hose (python) in the tank. I open the valve to the filter to fully open (Sometimes I hit the priming button, sometimes not)
4) Water should start to prime the filter properly (eliminating any air bubbles that stick around like when you install a full filter) - WATCH OUT for air and water spray rocketing out of the spray bar! (it only lasts a second). You'll hear water rushing into the filter.
5) Top off the water to the tank, and remove the refill hose.
6) Once you hear the water stop flowing into the filter, Turn it on. You may need to hit the priming button once more, but you'll feel the flow start to speed up.
7) Adjust the valve to your required speed and you're good to go.
IF you're priming it for the first time and don't have any water in your intake hose..... Install the filter, close the main valve, fill the tank to the top, open the cap on the intake and use a turkey baster to fill the intake hose. Close off the cap, Make sure the water is very high in the tank, and repeats steps 3-7.
* If you have to either remove the filter for cleaning, or drop the water line below the intake basket, just make sure the intake hose stays full (with the valve closed of course), and refill to the top (shut off the water) and do points 2 thru 7. If you're doing huge water changes (Like a bottomless discus tank) then I suggest a couple large sponge filters.
You're right. The instructions are brutal. Make sure you move the valve actuator slowly. Its plastic and I've broken two of them. Once they're stuck in there, it can (sometimes) sacrifice the whole head unit. Lots of initial headaches, but I'm at 3 years going strong.