I don't ever vacuum the poop, I just leave it and eventually it disappears, thinking maybe it goes to poop heaven.
I use the aquen changer similar to the python, with the plastic tube it's useless for vacuuming. I discovered the longer the tube the less it can pick up. Using the hose without the tube seems to work better, but you pick up sand too. How are you starting the siphon off a 50 ft hose ? I can never get any siphon without it connected to the faucet and running water, unless I'm using the regular hose that doesn't connect to faucet which is only a few feet. Are you sucking the other end because I think that's disgusting.